A new book traces the multi-racial bloodline of U.S. first lady Michelle Obama over five generations – finding that she descended from white Irish immigrants.

Author of American Tapestry: The Story of the Black, White and Multiracial Ancestors of Michelle Obama Rachel Swarns told CTV News Channel she used DNA testing to fill the missing links in the U.S. president’s wife’s ancestry.

“Mrs. Obama has long suspected she had white ancestry,” said Swarns, a New York Times reporter. “What I was able to do in this book is to dig back into history using DNA testing and research to actually indentify the white ancestry in the family tree.”

She eventually indentified a DNA match between Michelle Obama’s great-great-great grandmother, a slave named Melvina, and her great-great-great grandfather, who Swarns said was a white slave owner.

“Imagine someone knocking on your door and telling you, ‘By the way your family long ago owned the first lady’s family,’” said Swarns.

She said she received a very mixed reaction from the members of Michelle Obama’s lineage she contacted during her research.

“On the one hand, as you might imagine, it’s kind of amazing to be related to someone in the White House. On the other hand, these connections date back to a really painful period in our history.

“Some people were fascinated and interested and happy to be interviewed. Other people were uncomfortable and unsettled by this kind of connection.”

Asked if the findings in “American Tapestry” would help heal or further aggregate the country’s racial divide, Swarns said she believes the book will shine a spotlight on the interconnectedness of Americans.

“Lots of people are making these discoveries on their own. DNA testing is much more popular these days. People are digging into their family tree and making these discoveries. This is unchartered terrain in many ways.”

However, Swarns added that some of the details in “American Tapestry,” released Tuesday, are difficult to process.

“It’s hard to think of people owning other human beings. It’s hard to think what may have happened to that salve girl, whether she was raped or not. But it is our history...When you look at Michelle Obama in the White House it also shows you how far we’ve come.”

Swarns said she gave the White House a copy of the book ahead of publication but she’s yet to receive any reaction from the first lady or her staff.

“(Michelle Obama) said she finds her history fascinating. And I think many Americans will find it fascinating.”