In the post, Roberts thanked her longtime girlfriend, Amber Laign.
The message, which follows Roberts' battle with a life-threatening illness, is the first time the anchor has publicly acknowledged her same-sex relationship with Laign, a massage therapist from the San Francisco Bay Area.
Roberts wrote the post reflecting on a year ago when she reached the 100-day mark after undergoing a bone marrow transplant. The post was confirmed by ABC News spokesperson Heather Riley.
The TV news anchor has been open with her family, friends and co-workers about her sexuality. She and Laign have been together for a decade.
Sunday was the anniversary of Roberts' 100-day milestone following a bone marrow transplant in September 2012 for treatment of myelodysplastic syndrome, a rare blood and bone marrow disease.
In May, Grand Central Publishing announced Roberts, one of the most popular figures in morning TV news, will write a memoir about her battle with MDS and the life lessons she continues to gather following her return to "GMA" last February.
Sunday's post thanked everyone who helped her through her recovery.
The Associated Press contributed to this report.
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