Earlier Monday, Britain's royal palace confirmed the baby's arrival on Twitter. The baby is the third child for Kate and husband Prince William and fifth in line to the throne.
The baby, whose name has yet to be announced, weighed 8 pounds, 7 ounces and was born at 11:01 a.m. (6:01 a.m. ET|3:01 a.m. PT).
The 36-year-old duchess and her husband had traveled by car from their Kensington Palace home to the private Lindo Wing of St. Mary's Hospital in central London.
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William and Kate married in 2011 and have two other children: Prince George, 4, and Princess Charlotte, who turns 3 next month. Both were born at the same hospital, as were William and his younger brother Prince Harry.
RAW VIDEO: Prince George and Princess Charlotte arrive at hospital to meet baby brother
Prince George and Princess Charlotte arrive to meet their new brother
The baby is Queen Elizabeth II's sixth great-grandchild, in line to the throne after grandfather Prince Charles, father Prince William and the two older siblings. The new arrival bumps Prince Harry to sixth place in the line of succession.
RELATED: How two royal babies and two royal weddings in 2018 affect the line of succession
What do two royal weddings and two royal babies mean for the line to the British throne?
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The baby arrives just a few weeks before the wedding of uncle Harry to Meghan Markle on May 19.
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In a mix of royal tradition and modernity, the birth was announced with a notice placed on an easel in the forecourt of Buckingham Palace - and on royal social media accounts.
Many are betting on a traditional royal name for the baby. Monday is St. George's Day, England's national day, but the name is already taken by the baby's big brother.
Like its older siblings, the baby's full title will be Her (or His) Royal Highness, Princess (or Prince), followed by several given names.
PHOTOS: William, Kate and their family through the years
The Duchess of Cambridge during a visit to Evelina Children's Hospital in London on Tuesday, December 11, 2018.none
The bridesmaids and page boys, including Prince George and Princess Charlotte, arrive for the wedding of Princess Eugenie of York and Jack Brooksbank on Oct. 12, 2018none
Prince George and Princess Charlotte arrive for the the wedding of Princess Eugenie of York and Jack Brooksbank at St George’s Chapel, Windsor Castle on Oct. 12, 2018.none
Kate, Duchess of Cambridge carries Prince Louis as they arrive for his christening service at the Chapel Royal, St James's Palace, London, Monday, July 9, 2018.none
Princess Charlotte and Prince George hold the hands of their father Prince William while Kate, Duchess of Cambridge holds Prince Louis as they arrive for his christening service.none
Kate, Duchess of Cambridge carries Prince Louis as they arrive for his christening service at the Chapel Royal, St James's Palace, London, Monday, July 9, 2018.none
Prince George of Cambridge attends the Maserati Royal Charity Polo Trophy at Beaufort Park on June 10, 2018 in Gloucester, England.none
Catherine, Duchess of Cambridge and Princess Charlotte of Cambridge attend the Maserati Royal Charity Polo Trophy at the Beaufort Polo Club on June 10, 2018 in Gloucester, England.none
Kate, Prince George of Cambridge and Princess Charlotte of Cambridge attend the Maserati Royal Charity Polo Trophy at Beaufort Park on June 10, 2018 in Gloucester, England.none
Kate, Duchess of Cambridge with their newborn baby son as they leave the Lindo wing at St Mary's Hospital in London London, Monday, April 23, 2018.none
Britain's Prince William arrives with Prince George and Princess Charlotte back to the Lindo wing at St Mary's Hospital in London London, Monday, April 23, 2018.none
Prince William and Kate, Duchess of Cambridge wave holding their newborn baby son as they leave the Lindo wing at St Mary's Hospital in London London, Monday, April 23, 2018.none
Queen Elizabeth II, with Prince William and Kate, Duchess of Cambridge, leave the annual Easter Sunday service at St George's Chapel at Windsor Castle in Windsor on April 1, 2018.none
Britain's Kate, Duchess of Cambridge visits Sports Aid with Prince William at the Copperbox Arena in London, Thursday March 22, 2018.none
Britain's Kate Duchess of Cambridge taking part in preparations for a Commonwealth Big Lunch at St Luke's Community Centre, London, Thursday March 22, 2018.none
Britain's Kate, the Duchess of Cambridge, smiles as she visits the 1st Battalion Irish Guards, for the St. Patrick's Day Parade in Hounslow, England, March 17, 2018.none
Britain's Prince William, Kate the Duchess of Cambridge, Meghan Markle and Britain's Prince Harry arrive for the Commonwealth Service at Westminster Abbey on March 12, 2018.none
The Duchess of Cambridge interacts with Diane Leach and her daughter Tilly, during a visit to Pegasus Primary School in Oxford.none
Britain's Kate, Duchess of Cambridge, right, with Prince Harry and his fiancee Meghan Markle attend the first annual Royal Foundation Forum in London, Wednesday Feb. 28, 2018.none
Britain's Kate Duchess of Cambridge jokes about being pregnant while visiting the Fire Station arts center in Sunderland northeast England Wednesday Feb. 21, 2018.none
Britain's Kate, the Duchess of Cambridge and William, Duke of Cambridge arrive with Chief Executive of BAFTA Amanda Berry at the BAFTA Awards 2018 in London, Sunday, Feb. 18, 2018.none
Britain's Princess Kate Duchess of Cambridge, and Crown Princess Victoria of Sweden, talk during their visit at the Karolinksa Institute in Solna, Sweden, Wednesday Jan. 31, 2018.none
Kate tries a shot with a bandy stick in Stockholm, Sweden, Tuesday Jan. 30, 2018, during Prince William and Duchess of Cambridge 4-day visit to Sweden and Norway.none
Britain's Kate, Duchess of Cambridge, arrives to meet patients and staff at the Mother and Baby unit at the Bethlem Royal Hospital in south London, Wednesday, Jan. 24, 2018.none
Kate meets with graduates during her visit to The Maurice Wohl Clinical Neuroscience Institute, at King's College in London, Wednesday Jan. 24, 2018.none
Britain's Kate, the Duchess of Cambridge gestures to patient Rafael Chana, 4, as she visits Great Ormond Street Hospital on Jan. 17, 2018.none
Kate, Duchess of Cambridge smiles as she interacts with children Wednesday Jan. 10, 2018 during a visit to the Reach Academy Feltham, in London.AP
Prince William and Kate, the Duchess of Cambridge attend the Children's Global Media Summit at the Manchester Central Convention Complex in Manchester, England, Dec 6, 2017.none
Kate, Duchess of Cambridge arrives Jan. 10, 2018 for a visit to the Reach Academy Feltham in London.AP
Kate attends a reception at Buckingham Palace, London, to celebrate World Mental Health Day, Tuesday Oct. 10, 2017.none
Prince George arrives for his first day of school at Thomas's school in Battersea and is met by Helen Haslem head of the lower school.Creative Content
Britain's Prince William accompanies Prince George as he is greeted by Helen Haslem - the head of the lower school as he arrives for his first day of school.Creative Content
Prince George of Cambridge, Prince William, Duke of Cambridge, Catherine, Duchess of Cambridge and Princess Charlotte of Cambridge depart from Hamburg airport on July 21, 2017.Creative Content
Prince William, Duke of Cambridge, Catherine, Duchess of Cambridge and Prince Harry visit The Sunken Garden at Kensington Palace on August 30, 2017 in London, England.Creative Content
Kate, the Duchess of Cambridge boards a plane with her daughter Charlotte in Hamburg, Germany, Friday, July 21, 2017.AP
Prince William and his wife Kate, the Duchess of Cambridge, and their children, Prince George, and Princess Charlotte board a plane in Hamburg, Germany, Friday, July 21, 2017.AP
Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge at the Wall of Remembrance as they visit the Warsaw Rising Museum which is dedicated to the uprising of 1944.Creative Content
Catherine, Duchess of Cambridge, Princess Charlotte of Cambridge, Prince William, Duke of Cambridge and Prince George of Cambridge arrive at Warsaw airport during an official visitCreative Content
President Andrzej Duda and the First Lady Agata Kornhauser-Duda greet Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge at the Presidential Palace.Creative Content
The royal family appears on the balcony of Buckingham Palace, after attending the annual Trooping the Colour Ceremony in London, Saturday, June 17, 2017.none
The royal family appears on the balcony of Buckingham Palace, after attending the annual Trooping the Colour Ceremony in London, Saturday, June 17, 2017.none
The royal family appears on the balcony of Buckingham Palace, after attending the annual Trooping the Colour Ceremony in London, Saturday, June 17, 2017.none
The royal family appears on the balcony of Buckingham Palace, after attending the annual Trooping the Colour Ceremony in London, Saturday, June 17, 2017.none
Catherine, Duchess of Cambridge receives flowers from a boy at Place Clairefontaine during a one day visit to Luxembourg on May 11, 2017 in Luxembourg, Luxembourg.none
Catherine, Duchess of Cambridge receives flowers from a boy at Place Clairefontaine during a one day visit to Luxembourg on May 11, 2017 in Luxembourg, Luxembourg.none
Catherine, Duchess of Cambridge feeds a lamb as she visits Farms for City Children on May 3, 2017 in Arlingham, Gloucestershire.Creative Content
A photo released by the Duke and Duchess of Cambridge shows their daughter, Princess Charlotte, taken in April 2017 by her at Anmer Hall in Norfolk, England.AP
Kate, the Duchess of Cambridge meets Dion and Danielle with baby Mia during a visit to the Ronald McDonald House Evelina in London, Tuesday, Feb. 28, 2017.none
Kate, the Duchess of Cambridge smiles while talking to a child during a visit to the Ronald McDonald House Evelina in London, Tuesday, Feb. 28, 2017.none
Duchess Kate visited the Evelina London Children's Hospital on Feb. 28. According to ABC News she wore a blue, fringed Rebecca Taylor peplum suit.none
Britain's Kate, the Duchess of Cambridge receives a bouquet of flowers as she arrives at Ronald McDonald House Evelina, in London, Tuesday, Feb. 28, 2017.none
Princess Kate and Prince William arrive at the British Academy Film Awards in London, Sunday, Feb. 12, 2017.none
Princess Kate and Prince William arrive at the British Academy Film Awards in London, Sunday, Feb. 12, 2017.none
Britain's Prince William speaks with Aoife, 9, during his visit to a Child Bereavement UK Centre in Stratford in east London, Wednesday, Jan. 11.none
Kate the Duchess of Cambridge speaks to families who have experienced bereavement during their visit to a Child Bereavement UK Centre in Stratford in east London on Jan. 11.none
Britain's Prince William and Kate the Duchess of Cambridge prepare to cut a cake to celebrate the one year anniversary of this charity's branch on Jan. 11.none
The royal family arrives for the annual evening reception for members of the Diplomatic Corps at Buckingham Palace on December 8, 2016 in London, England.none
Catherine, Duchess of Cambridge departs after attending the annual Diplomatic Reception at Buckingham Palace on December 8, 2016 in London, England.none
Diana, Princess of Wales during a tour of Hong Kong on Nov. 10, 1989 (left) and Catherine, Duchess of Cambridge on Dec. 8, 2016 in London.none
Two Welsh Pembrokeshire Corgi dogs sit on a chair in front of wax work models of the British Royal family wear colorful Christmas themed jumpers for a charity campaign.none
Welsh Pembrokeshire Corgi pose with wax models of the British Royal family wearing colorful Christmas themed jumpers for a charity campaign.none
Welsh Pembrokeshire Corgi pose with wax models of the British Royal family wearing colorful Christmas themed jumpers for a charity campaign.none
Catherine, the Duchess of Cambridge, arrives at Working Titles Office, to see 'A Street Cat Named Bob' in London, Thursday, Nov. 3, 2016none
Catherine, Duchess of Cambridge, arrives at Working Titles Office, to see 'A Street Cat Named Bob' in London, Thursday, Nov. 3, 2016.none
Catherine, Duchess of Cambridge, greets Bob the cat as she attends the UK Premiere of 'A Street Cat Named Bob' in aid of Action On Addiction on November 3, 2016 in London, England.none
Prince William and Kate, Duchess of Cambridge at a reception for Olympians and Paralympians hosted by Britain's Queen Elizabeth II on October 18, 2016.AP
Britain's Prince William kicks a football in the simulator, watched by Kate, Duchess of Cambridge, Friday Oct. 14, 2016, at The National Football Museum, in Manchester, England.AP
Prince William, Kate Duchess of Cambridge, and Prince Harry take a ride in a pod of the London Eye with members of the mental health charity "Heads Together" on October 10, 2016.AP
Britain's Kate, the Duchess of Cambridge sits in on a class during a visit to the Stewards Academy on September 16, 2016.AP
Britain's Kate, the Duchess of Cambridge meets parents, during a visit to the Stewards Academy with Prince William as part of their "Heads Together' campaign on September 16, 2016.AP
Britain's Prince William, Duke of Cambridge, learns a dance move with Scariofunk dance collective during a visit to Caius House Youth Centre in London Wednesday, Sept. 14, 2016.AP
Britain's Prince William, Duke of Cambridge, meets young people in a boxing ring whilst on a visit to Caius House Youth Centre in London Wednesday, Sept. 14, 2016.AP
Kate Middleton, Prince William, Canadian Prime Minister Justin Trudeau and Sophie Gregoire-Trudeau in Vancouver on September 25, 2016.none
Kate Middleton receives flowers during their visit to the Immigrant Services Society of British Columbia New Welcome Centre during their Royal Tour of Canada on September 25, 2016.none
Kate Middleton and Prince William meet a baby in Vancouver during a visit to Sheway, a charity that helps vulnerable mothers on September 25, 2016.none
Kate Middleton and Prince William with David Johnston, Government General of Canada and his wife Sharon Johnston at Government House on September 24, 2016 in Victoria, B.C.none
Prince William, Kate Middleton, Prince George of Cambridge and Princess Charlotte of Cambridge arrive at the Victoria Airport in British Columbia on September 24, 2016.none
Prince George plays on a swing at Sandringham in Norfolk, England.none
Prince George plays with the family dog Lupo, at Sandringham in Norfolk, England.none
Prince George beckons for his mother Kate, the Duchess of Cambridge, after being lifted out of a Squirrel helicopter by his father, Prince William on Friday, July 8, 2016.AP
Prince George, wears ear defenders as he visits with his father Prince William the Royal International Air Tattoo at RAF Fairford in England, Friday, July 8, 2016.AP
Prince George, is lifted out of the cockpit of a red plane by his father Prince William as they visit the Royal International Air Tattoo at RAF Fairford in England, July 8, 2016.AP
Prince George looks up at a helicopter as he visits the Royal International Air Tattoo at RAF Fairford in England on July 8, 2016.AP
Kate, the Duchess of Cambridge, front right, applauds in the Royal Box on day eleven of the Wimbledon Tennis Championships in London, Thursday, July 7, 2016.AP
Prince George meets President Barack Obama and First Lady Michelle Obama.none
The royal family with President Barack Obama and Michelle Obama.none
Bhutan's king Jigme Khesar Namgyel Wangchuk, Bhutan's queen, Jetsun Pema, Prince William and Kate are seen inside a Buddhist temple in Thimphu, Bhutan, Thursday, April 14, 2016.AP
Bhutan's king Jigme Khesar Namgyel Wangchuk, Bhutan's queen, Jetsun Pema, Prince William and Kate are seen in Thimphu, Bhutan, Thursday, April 14, 2016.AP
Bhutan's queen, Jetsun Pema, Bhutan's king Jigme Khesar Namgyel Wangchuk, Prince William and Kate pose for a photograph in Thimphu, Bhutan, April 14, 2016.AP
Britain's Prince William and his wife Kate, Duchess of Cambridge are seen in Thimphu, Bhutan, Thursday, April 14, 2016.AP
Britain's Prince William and his wife Kate, Duchess of Cambridge are seen in Thimphu, Bhutan, Thursday, April 14, 2016.AP
Kate, Duchess of Cambridge, is helped by Bhutan's King, Jigme Khesar Namgyel Wangchuk, as she lights up an oil lamp in Thimphu, Bhutan, Thursday, April 14, 2016.AP
Bhutan's King Jigme Khesar Namgyel Wangchuk, Bhutan's Queen, Jetsun Pema, Kate and Prince William pose for a photograph in Thimphu, Bhutan, April 14, 2016.AP
Bhutan's King Jigme Khesar Namgyel Wangchuk, Bhutan's Queen, Jetsun Pema, Kate and Prince William pose for a photograph in Thimphu, Bhutan, Thursday, April 14, 2016.AP
Britain's Prince William left, walks with Bhutan's king, Jigme Khesar Namgyel Wangchuk, in Thimphu, Bhutan, Thursday, April 14, 2016.AP
Prince William and his wife Kate walk at the Centre for Wildlife Rehabilitation and Conservation at Panbari reserve forest in northeastern Assam state, India, April 13, 2016.AP
Prince William and his wife Kate prepare to set off on a jeep safari at Kaziranga National Park, northeastern Assam state, India Wednesday, April 13, 2016.AP
Prince William and his wife Kate talk to officials at the Centre for Wildlife Rehabilitation and Conservation on April 13, 2016.AP
Prince William and his wife Kate greet children of Panbari village at the Centre for Wildlife Rehabilitation and Conservation on April 13, 2016.AP
Indian villagers facilitate Kate with a Gamocha, a traditional shawl at Panbari village in Kaziranga, east of Gauhati, northeastern Assam state, India, April 13, 2016.AP
Kate gives a finishing touch of paint on a statue of elephant at the Centre for Wildlife Rehabilitation and Conservation (CWRC) on April 13, 2016.AP
Prince William and his wife Kate interact with children of Panbari village at the Centre for Wildlife Rehabilitation and Conservation (CWRC) on April 13, 2016.AP
Kate walks with baby rhinos at at the Centre for Wildlife Rehabilitation and Conservation (CWRC) at Panbari reserve forest on April 13, 2016.AP
Kate feeds a baby elephant at at the Centre for Wildlife Rehabilitation and Conservation (CWRC) at Panbari reserve forest in northeastern Assam state, India on April 13, 2016.AP
Prince William and Kate visit a village tea garden in Kaziranga, east of Gauhati, northeastern Assam state, India, Wednesday, April 13, 2016.AP
Prince William and Kate take an open vehicle safari inside the Kaziranga National Park, east of Gauhati, northeastern Assam state, India, Wednesday, April 13, 2016.AP
Prince William and Kate take an open vehicle safari inside the Kaziranga National Park, east of Gauhati, northeastern Assam state, India, Wednesday, April 13, 2016.AP
Prince William and Kate feed baby elephants at the Centre for Wildlife Rehabilitation and Conservation in northeastern Assam state, India, Wednesday, April 13, 2016.AP
Kate feeds a baby elephant at the Centre for Wildlife Rehabilitation and Conservation in northeastern Assam state, India, Wednesday, April 13, 2016.AP
Kate feeds a baby elephant at the Centre for Wildlife Rehabilitation and Conservation in northeastern Assam state, India, Wednesday, April 13, 2016.AP
Kate feeds a baby rhino at the Centre for Wildlife Rehabilitation and Conservation in northeastern Assam state, India, Wednesday, April 13, 2016.AP
Prince William and Kate board a jeep for a safari at Kaziranga National Park, east of Gauhati, northeastern Assam state, India Wednesday, April 13, 2016.AP
Indian villagers facilitate Britain's Prince William with a Gamocha, a traditional shawl as his wife, Kate, watches at Panbari village in Kaziranga, India, April 13, 2016.AP
Prince William, along with his wife, Kate, interact with villagers at Panbari village, east of Gauhati, northeastern Assam state, India on April 13, 2016.AP
Prince William along with his wife Kate watch a traditional dance at Panbari village, east of Gauhati, northeastern Assam state, India on April 13, 2016.AP
Prince William and Kate come out after visiting “Naamghar” Assamese Holy Place at Panbari village, east of Gauhati, northeastern Assam state, India, Wednesday, April 13, 2016.AP
An Indian woman presents a hand woven cloth to Kate, the Duchess of Cambridge, in Panbari village, east of Gauhati, northeastern Assam state, India, Wednesday, April 13, 2016.AP
Prince William and Kate pose with forest officials in the Kaziranga National Park, east of Gauhati, northeastern Assam state, India, April 13, 2016.AP
Prince William and Kate watch Assamese traditional dancers perform in Diphlu River Lodge, east of Gauhati, northeastern Assam state, India, April 12, 2016.AP
Prince William and Kate interact with a very young Assamese traditional Bihu dancer in Diphlu River Lodge, east of Gauhati, northeastern Assam state, India, April 12, 2016.AP
Prince William, signs visitor's book as his wife Kate, the Duchess of Cambridge looks on after paying their tributes at the India Gate war memorial on April 11, 2016.AP
AP
Prince William and wife Kate, the Duchess of Cambridge, paying their tributes at the India Gate war memorial on April 11, 2016.AP
The wreath which was placed by Britain's Prince William, and his wife Kate, the Duchess of Cambridge at the India Gate war memorial in New Delhi, India, Monday, April 11, 2016.AP
Prince William, along with his wife Kate, the Duchess of Cambridge leaves after paying their tributes at the India Gate war memorial in New Delhi, India, Monday, April 11, 2016AP
Prince William and wife Kate, the Duchess of Cambridge, paying their tributes at the India Gate war memorial on April 11, 2016.AP
Prince William, along with his wife Kate, the Duchess of Cambridge leaves after paying their tributes at the India Gate war memorial in New Delhi, India, Monday, April 11, 2016AP
Prince William and Kate, the Duchess of Cambridge, walk together during a visit to Gandhi Smiriti, an Indian museum dedicated to Mahatma Gandhi, on April 11, 2016.AP
Prince William, the Duke of Cambridge, and his wife Kate, the Duchess of Cambridge, remove their shoes ahead of paying tribute during a visit to Gandhi Smiriti on April 11, 2016.AP
Prince William, the Duke of Cambridge, and his wife Kate, the Duchess of Cambridge, remove their shoes ahead of paying tribute during a visit to Gandhi Smiriti on April 11, 2016.AP
Britain's Prince William, along with his wife Kate, the Duchess of Cambridge, centre, arrive to pay their tributes at the India Gate war memorial on April 11, 2016,AP
Britain's Prince William, along with his wife Kate, the Duchess of Cambridge pose for the media after paying their tributes at the India Gate war memorial on April 11, 2016.AP
Britain's Prince William, along with his wife Kate, the Duchess of Cambridge leave after paying their tributes at the India Gate war memorial on April 11, 2016.AP
Britain's Prince William, along with his wife Kate, the Duchess of Cambridge leave after paying their tributes at the India Gate war memorial on April 11, 2016.AP
Britain's Prince William, along with his wife Kate, the Duchess of Cambridge, right, pay their tributes at the India Gate war memorial on April 11, 2016.AP
AP
Prince William eats a "dosa", or a rice pancake as his wife Kate, the Duchess of Cambridge, watches during an event on young entrepreneurs in Mumbai, India, Monday, April 11, 2016.AP
Britain's Prince William steers a Formula E simulator at an event on young entrepreneurs in Mumbai, India, Monday, April 11, 2016.AP
Prince William and his wife Kate, the Duchess of Cambridge, remove their shoes before paying homage to Mahatma Gandhi during a visit to ''Gandhi Smriti'' in on April 11, 2016.AP
Prince William along with his wife Kate, the Duchess of Cambridge walk as they pay tribute during a visit to Gandhi Smiriti on April 11, 2016.AP
Britain's Prince William, along with his wife Kate, the Duchess of Cambridge interact with school children during a visit to Gandhi Smiriti on April 11, 2016.AP
Prince William along with his wife Kate, the Duchess of Cambridge speak to each other as they pay tribute during a visit to Gandhi Smiriti on April 11, 2016.AP
rince William, right, eats a "dosa" or a rice pancake as his wife Kate, the Duchess of Cambridge, watches during an event on young entrepreneurs in Mumbai, India, April 11, 2016.AP
Britain's Kate, the Duchess of Cambridge, plays cricket at Oval Maidan in Mumbai, India, Sunday, April 10, 2016.AP
Prince William, and his wife, Kate, the Duchess of Cambridge, pose after they arrive for a charity ball at the Taj Mahal Palace hotel in Mumbai, India, Sunday, April 10, 2016.AP
Britain's Prince William, and his wife Kate, the Duchess of Cambridge, greet people as they leave after their visit to a slum in Mumbai, India, Sunday, April 10, 2016.AP
Prince William, watches as his wife Kate, the Duchess of Cambridge, plays soccer during their visit to a slum in Mumbai, India, Sunday, April 10, 2016.AP
Britain's Prince William, plays soccer as his wife Kate, the Duchess of Cambridge, watches during their visit to a slum in Mumbai, India, Sunday, April 10, 2016.AP
Britain's Prince William, plays soccer as his wife Kate, the Duchess of Cambridge, watches during their visit to a slum in Mumbai, India, Sunday, April 10, 2016.AP
The Duke and Duchess of Cambridge, Prince William, and his wife Kate, are garlanded as they arrive at the Banganga Water Tank in Mumbai, Sunday, April 10, 2016AP
The Duke and Duchess of Cambridge, Prince William, and his wife, the former Kate Middleton, float flowers at the Banganga Water Tank in Mumbai, India, Sunday, April 10, 2016AP
The Duchess of Cambridge, the former Kate Middleton, plays with Indian children during a charity event at the Oval Maidan in Mumbai, India, Sunday, April 10, 2016.AP
Britain's Kate, the Duchess of Cambridge, plays cricket at Oval Maidan in Mumbai, India, Sunday, April 10, 2016.AP
Prince William, center in white, and his wife Kate, walk with officials during a charity event at the Oval Maidan in Mumbai, India, on April 10, 2016.AP
The Duke and Duchess of Cambridge, Prince William, and his wife Kate, stand after laying a wreath at the Taj Mahal Palace Hotel in Mumbai, India on April 10, 2016.none
The Duke and Duchess of Cambridge, Prince William, and his wife, the former Kate Middleton lay a wreath on the martyrs memorial at the Taj Mahal Palace Hotel, April 10, 2016.AP
Britain's Prince William, left, along with Kate, the Duchess of Cambridge, talks with staff members at Hotel Taj in Mumbai, India, Sunday, April 10, 2016.AP
The royal family goes skiing in the French Alps on March 3, 2016. It was their first vacation as a family of four.none
Prince William, right, and Kate the Duchess of Cambridge pose with their children, Princess Charlotte, centre left, and Prince George while on vacation in the French Alps.none
Britain's Prince William poses with daughter Princess Charlotte while skiing in the French Alps on March 3, 2016.none
Britain's Prince William and Kate Duchess of Cambridge enjoy a snow ball fight in the French Alps on March 3, 2016.none
Prince William and Kate Duchess of Cambridge walk together while on vacation in the French Alps on March 3, 2016.none
Prince William and Kate Duchess of Cambridge enjoy a snow ball fight while on vacation in the French Alps on March 3, 2016.none
Britain's Prince George poses on his first day at the Westacre Montessori nursery school near Sandringham in Norfolk, England on Jan. 6, 2016.none
Britain's Prince George poses on his first day at the Westacre Montessori nursery school near Sandringham in Norfolk, England on Jan. 6, 2016.none
Britain's Kate Duchess of Cambridge visits the Anna Freud Centre in London on Sept. 17, 2015, in her first public engagement since Charlotte's birth.none
Britain's Kate Duchess of Cambridge visits the Anna Freud Centre in London on Sept. 17, 2015, in her first public engagement since Charlotte's birth.none
Britain's Kate Duchess of Cambridge visits the Anna Freud Centre in London on Sept. 17, 2015, in her first public engagement since Charlotte's birth.none
Britain's Kate Duchess of Cambridge visits the Anna Freud Centre in London on Sept. 17, 2015, in her first public engagement since Charlotte's birth.none
Britain's Kate Duchess of Cambridge visits the Anna Freud Centre in London on Sept. 17, 2015, in her first public engagement since Charlotte's birth.none
This photo of Prince George and Prince William was released in honor of George's second birthday on July 22. The photo was taken at the christening of Princess Charlotte.none
Prince William and his wife, Kate, pose for a photo with their children after the christening of Princess Charlotte at the Sandringham Estate on July 5, 2015.none
Prince William and his wife Kate, the Duchess of Cambridge, pose for a photo with their families after the christening of their daughter Princess Charlotte on July 5, 2015.none
Catherine, Duchess of Cambridge, and her daughter Princess Charlotte pose for a photo in the drawing room at Sandringham House after the christening.none
Britain's Prince George peeks into the pram of Princess Charlotte flanked by his parents in Sandringham, England, July 5, 2015.none
Britain's Prince William, Kate the Duchess of Cambridge, their son Prince George and daughter Princess Charlotte at St. Mary Magdalene Church in Sandringham, England, July 5, 2015.none
Britain's Queen Elizabeth II stands with Kate the Duchess of Cambridge whilst pushing Princess Charlotte at St. Mary Magdalene Church in Sandringham, England, July 5, 2015.none
Britain's Princess Charlotte is pushed in a pram after her christening at St. Mary Magdalene Church in Sandringham, England, July 5, 2015.none
Three generations of princes -- George, William and Charles -- appeared on the balcony of Buckingham Palace during Queen Elizabeth II's birthday parade in June 2015.none
This photo of Britain's Princess Charlotte, held by her brother Prince George, was released by Kensington Palace Saturday, June 6, 2015.none
This photo of Britain's Princess Charlotte, held by her brother Prince George, was released by Kensington Palace Saturday, June 6, 2015.none
This image shows Britain's Princess Charlotte, right, being held by her brother, 2-year-old, Prince George.none
Princes George and Prince William wave as they return to St. Mary's Hospital on May 2, 2015, the day Charlotte was born.none
The Lindo Wing of St Mary's Hospital, London. Britain's Kate the Duchess of Cambridge is expected to give birth to her second child at the hospital in the coming weeks.AP
Royal fan Tarry Hutt sits outside St Mary's Hospital, in anticipation of Kate, Duchess of Cambridge having her second child, Wednesday, April 22, 2015.AP
Royal fans wait outside the Lindo Wing at St Mary's Hospital, April 20, 2015. Kate, Duchess of Cambridge is expected to give birth to her second child there later this month.AP
Britain's Duke of Cambridge and Duchess of Cambridge leave St Paul's Cathedral, in central London, Friday, March 13, 2015.AP
Britain's Kate, Duchess of Cambridge arrives at the Resort Studios, Cliftonville, Margate, Wednesday March 11, 2015.AP
Britain's Kate, Duchess of Cambridge, laughs during her visit to Cape Hill Children's Centre, Smethwick, central England, Wednesday, Feb. 18, 2015.AP
Britain's Kate, Duchess of Cambridge, waves as she arrives to attend a coffee morning at Family Friends, in Kensington, London, Monday Jan. 19, 2015.AP
Britain's Prince William, left, and Kate, the Duchess of Cambridge, tour the lobby of One World Trade Center, Tuesday, Dec. 9, 2014 in New York.AP
Prince William, the Duke of Cambridge, and Kate, the Duchess Of Cambridge, at British Consul General's Residence, Monday, December 08, 2014 in New York.AP
Britain's Kate, Duchess of Cambridge attends the Place2be Wellbeing in Schools Award at Kensington Palace, London Wednesday, Nov. 19, 2014.AP
Catherine Duchess of Cambridge arrives at the Natural History Museum in London, Tuesday, Oct. 21, 2014 for the Wildlife Photographer of the Year 2014 awards ceremony.AP
This photo of Prince George walking was released for his first birthday. It was taken at the Sensational Butterflies exhibition at the Natural History Museum in London.none
The Duke and Duchess of Cambridge arrive for a ceremony to mark the 100th anniversary of the outbreak of World War I in St. Symphorien, Belgium on Monday, Aug. 4, 2014.AP
Britain's Kate, Duchess of Cambridge arrives at the National Maritime Museum in Greenwich, London, Tuesday, June 10, 2014.AP
Their Royal Highnesses Prince William right, Kate, Duchess of Cambridge, and Prince George walk on the tarmac after they arrived in Sydney, Australia, Wednesday, April 16, 2014.AP
Britain's Kate, the Duchess of Cambridge, waves after a Palm Sunday service at the Cathedral in Dunedin, New Zealand, Sunday, April 13, 2014.AP
Britain's Prince George plays during a visit to Plunket nurse and parents group at Government House in Wellington, New Zealand, Wednesday, April 9, 2014.AP
Britain's Prince William and Catherine, Duchess of Cambridge with Prince George arrive at the International Airport, Wellington, New Zealand, Monday, April 07, 2014.AP
Kate, The Duchess of Cambridge during a visit to the 1st Battalion Irish Guards at the St. Patrick's Day Parade at Mons Barracks, Aldershot, in England, Monday, March 17, 2014.AP
Kate, The Duchess of Cambridge arrives at a Reception for the Dramatic Arts, at Buckingham Palace, London, Monday, Feb. 17, 2014.AP
Kate Duchess of Cambridge carries her son Prince George after his christening at the Chapel Royal in St James's Palace in London, Wednesday Oct. 23, 2013.AP
Britain's Kate, The Duchess of Cambridge waves as she leaves Queen Elizabeth Olympic Park in London, Friday, Oct. 18, 2013.AP
The Duchess of Cambridge and Duke of Cambridge carry the Prince of Cambridge outside for the first time at St Mary's Hospital in London, Monday, July 23, 2013.AP
Britain's Prince William and Kate, Duchess of Cambridge arrive to celebrate the 60th anniversary of the coronation of Britain's Queen Elizabeth II, Tuesday, June 4, 2013.AP
Britain's Duchess of Cambridge attends the National Review of Queen's Scouts at Windsor Castle, near London Sunday, April 21, 2013.AP
Britain's Kate Duchess of Cambridge smiles during her visit to the Emirates Arena in Glasgow, Scotland. Thursday April 4, 2013.AP
Britain's Kate, The Duchess of Cambridge arrives at Hope House, in London, Tuesday, Feb. 19, 2013.AP
The Duke and Duchess of Cambridge arrive for the UK Premiere of 'War Horse' at a central London cinema, London, Sunday, Jan. 8, 2012.AP
Britain's Prince William and his wife Kate, Duchess of Cambridge wave from the balcony of Buckingham Palace after the Royal Wedding in London Friday, April, 29, 2011.AP
Britain's Prince William kisses his wife Kate, Duchess of Cambridge on the balcony of Buckingham Palace after the Royal Wedding in London Friday, April, 29, 2011.AP
Britain's Prince William and his bride Kate, Duchess of Cambridge, leave Westminster Abbey, London, following their wedding, Friday April 29, 2011.AP
Britain's Prince William and his wife Kate, Duchess of Cambridge stand outside of Westminster Abbey after their Royal Wedding in London Friday, April, 29, 2011.AP
Britain's Prince William and Kate Middleton exchange rings in front of the Archbishop of Canterbury at Westminster Abbey, London, Friday April 29, 2011.AP
Kate Middleton arrives at Westminster Abbey at the Royal Wedding in London Friday, April 29, 2011.AP
Prince William and his wife Kate, Duchess of Cambridge stand outside of Westminster Abbey after their Royal Wedding in London Friday, April, 29, 2011.AP
Kate Middleton, left, arrives for her wedding at Westminster Abbey in London Friday, April 29, 2011.AP
Kate Middleton talks with staff during a visit to St Andrews University, St Andrews Scotland, Friday, Feb. 25 2011.AP
Kate Middleton arrives for a naming ceremony at Trearddur Bay Lifeboat Station in Anglesey, Wales, Thursday Feb. 24, 2011.AP
Britain's Prince William and his fiancee Kate Middleton at St. James's Palace in London, Tuesday Nov. 16, 2010, after they announced their engagement.AP
In this Sept. 17, 2009 file photo, Kate Middleton arrives at a charity disco in London.AP
Britain's Prince William and Kate Middleton, watch the England against Italy Six Nations rugby match at Twickenham stadium in London, Saturday Feb. 10, 2007.AP
Kate Middleton arrives at the Royal Military Academy, Sandhurst, where graduates, including the Prince, took part in the Sovereign's parade, Friday Dec. 15, 2006.AP
Kate Middleton leaves St Cyriac's Church, in Lacock, Wiltshire, England, Saturday May 6, 2006.AP
Kate Middleton leaves after attending their university graduation ceremony at St. Andrews University in St. Andrews, Scotland, Thursday, June 23, 2005.AP
The Prince of Wales, left, and his son Prince William hug each other during a photo call in Klosters, Switzerland, Sunday, March 28, 2004.AP
Britain's Prince William, wearing a Union Jack waistcoat, is seen in this 2000 photo in Eton, England.AP
Prince Charles accompanies his sons Prince William and Prince Harry to view tributes left in memory of their mother Princess Diana in London, Friday, Sept. 5, 1997.AP
The Royal Family pose in the White drawing room of Windsor Castle, on the day of Prince William's Confirmation, Sunday March 9 1997.AP
Princess Diana of Wales smiles as she sits with her sons, Princes Harry and William, on the steps of the Royal Palace on the island of Majorca, Spain, Aug. 9, 1987.AP
Britain's Prince William, the 6-month old son of Prince Charles and Princess Diana, with his parents at at Kensington Palace in London, England on Dec. 22, 1982.AP
Prince Charles, Prince of Wales, with his wife Princess Diana with their newborn son Prince William, as they leave St. Mary's Hospital in London, June 22, 1982.AP
The Associated Press contributed to this report.