Paula O'Brien, 39, said she posted to Facebook March 6 about when her brother put his first child up for adoption -- incorrectly giving the date as Sept. 19, 1982 -- and received a reply from Abbey Donohoe, 29, a woman she had befriended at a party four years earlier, the Quad City Times, Davenport, Iowa, reported Thursday.
"You sure it wasn't 1983? Because that's my birthday & I was adopted ... crazy!" Donohoe wrote.
The two women soon discovered it was more than a coincidence -- Donohoe was O'Brien's niece.
O'Brien said she and her family were overjoyed to welcome Donohoe back into the fold.
"It stayed with me all my life," O'Brien said. "I just always had this sense that she was out there. We've always observed her birthday, always had plans to find her. I wondered, 'Does she look like me?'"
O'Brien said her brother, who lives in Tennessee and has three children, is excited to meet his first daughter.
Celebrity Families of 2014 [PHOTOS]