First Lady Michelle Obama always suspected that she had white ancestors. But she had no idea who they were. With DNA testing and research, I was able to solve that mystery and finally identify the white forbears who had remained hidden in her family tree for more than a century.

All across the country, growing numbers of people are turning to DNA testing as a tool to help unlock the secrets of their roots, using companies such as Ancestry, among others. When I started researching my new book, “American Tapestry: The Story of the Black, White and Multiracial Ancestors of Michelle Obama,’’ I pored over historical documents that I found in local archives, courthouses and libraries as well as records that I found online on Ancestry and other state and local databases. But I knew that DNA testing would be the only way to unearth the truth.

I suspected that Mrs. Obama’s white ancestors belonged to the white Shields family that had owned her great-great-great-grandmother, Melvinia Shields. So I persuaded several descendants of the black and white Shields to do DNA testing.

The results showed that the two families were related. The DNA testing indicated that Melvinia’s owner’s son was the likely father of Melvinia’s biracial child, Dolphus Shields. (Dolphus Shields is the first lady’s great-great-grandfather.)

But last month, members of both sides of the family — black and white — put aside the pain of the past. They got together for the very first time in Rex, Georgia, at a ceremony to commemorate Melvinia’s life. They swapped family stories, posed for photographs, exchanged phone numbers and had a meal together.

It was something to see.

David Applin, who is Melvinia’s great-grandson, said the reunion was “wonderful.” And Jarrod Shields, who is the great-great-great-grandson of Melvinia’s owner, described it as a day “my family will never forget.”

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This story was contributed by guest blog author Rachel L. Swarns

Rachel L. Swarns has been a reporter for the New York Times since 1995. She has written about domestic policy and national politics, reporting on immigration, the presidential campaigns of 2004 and 2008, and First Lady Michelle Obama and her role in the Obama White House. She has also worked overseas for the New York Times, reporting from Russia, Cuba, and southern Africa, where she served as the Johannesburg bureau chief. She lives in Washington, D.C., with her husband and two children.

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