Middleton has not been seen publicly with Loudon, 30, for several weeks.
Instead, she's been seen around town -- and in Spain -- with former flame George Percy, son of the Duke of Northumberland, one of Britain's richest men.
As the duke's eldest son, Percy stands to inherit a considerable fortune.
"The Duke of Northumberland's son would be a considerable catch," said Charles Kidd, editor of the blue blood bible Debrett's Peerage. "He's the heir to his father and his father's title. The duke is the highest rank of the peerage -- they do rank just after the royal family."
Kidd said Percy, 27, has served as a "page of honor" to Queen Elizabeth II, a position that allows him to accompany the queen at some major state events.
Loudon also has "distinguished ancestry," Kidd said, with close ties to the 1st Earl Jellicoe, who served as admiral of the naval fleet.
Pippa Middleton's visits with Percy -- at a tennis tournament and a posh London restaurant -- have prompted Britain's newspapers to report that she and Loudon have separated.
Pippa Middleton, dubbed "her royal hotness" by the tabloids, has been in the news almost continuously since capturing attention at her sister's wedding to Prince William.
"I do think she's got the potential to be a huge star for years to come if she's very selective," said Max Clifford, Britain's most prominent publicist. "But I don't know who she's dating."