The White House has not yet commented on the research
Research into the family of US First Lady Michelle Obama has revealed that her great-great-great-grandmother was a slave given away at the age of six.
According to genealogist Megan Smolenyak, the girl was described in papers only as "negro girl Melvinia".
In her early teens, working as a slave on a farm in Georgia, she was made pregnant by an unknown white man.
The son she gave birth to around the year 1859, Dolphus, was Michelle's great-great grandfather.
Megan Smolenyak, whose discoveries have been detailed in the New York Times newspaper, said she was not surprised by what she discovered.
"But the fact that just 15 years after the death of Dolphus, one of his descendants was born who would end up in the White House, that is startling," she said.
The circumstances of Melvinia's first pregnancy are unclear, according to Ms Smolenyak. On the 1870 census, she is listed as having three mixed-race children, one born four years after emancipation.
"If you do African-American research that is not surprising at all - a lot of people don't appreciate how intermingled we are," Ms Smolenyak said.
According to her 1938 death certificate, the identity of Melvinia's parents was "unknown".
The White House has yet to comment on the research but Ms Smolenyak said she hoped the details of great-great grandparents Michelle Obama had perhaps not even heard of would "resonate".
She described how the slave girl and the son she bore seemed to want to be discovered.
"When you research a family, some call more loudly than others - it's like they want to be found. It was Melvinia and her son, Dolphus, that clearly wanted to be found," she said.