WASHINGTON » DNA testing all but confirmed Thomas Jefferson slept with his slave Sally Hemings. Now it’s rewriting another lurid chapter in presidential history, this one from the Roaring ’20s.

Genetic analysis has proved that President Warren G. Harding fathered a child with long-rumored mistress Nan Britton, according to AncestryDNA, a DNA-testing division of Ancestry.com.

Britton set off a Jazz Age sex scandal when she went public with her tale of forbidden love in the White House, boldly publishing her story in a 1927 best-selling memoir, "The President’s Daughter." But historians long questioned her claims, and Harding defenders vilified her as a liar for nearly 90 years.

Based on DNA from Britton’s grandson and descendants of Harding, the results are 99.9 percent certain, Ancestry.com said. The findings were first reported Thursday by The New York Times.

The child born of their union, Elizabeth Ann Blaesing, was the only known offspring of the 29th president. She died in 2005. Britton died in 1991.

James Blaesing, 65, who grew up hearing the story of his grandfather, the president, from Britton, his grandmother, told The Associated Press he long wanted to prove she was telling the truth. He was delighted by the DNA results.

"You know what this is? It’s a love story," he said of his grandparents. "It was true love, especially on her side, and I know he felt the same way. And he got trapped."

Harding was a heartthrob U.S. senator from Ohio when the affair began. Women found him handsome and charming with great magnetism. Britton was younger by 30 years and first developed a crush on Harding as a teenage girl in his hometown. The relationship continued when Harding was president, with Britton later writing of how they made love in a White House coat closet. The secret romance ended with Harding’s sudden death during his presidency in 1923.

Harding’s family long maintained Britton’s book was a lie or a childhood fantasy or was perhaps dreamed up by Democratic opponents of the Republican president. Some maintained that Harding was sterile because he had mumps as a child.

The Library of Congress recently published love letters from an earlier affair between Harding and another woman, Carrie F. Phillips, opening further doubts about the family’s denials.

Peter Harding of Big Sur, California, a grandnephew of the former president, wanted to know the truth, along with his cousin, Abigail Harding of Worthington, Ohio, who had already begun studying her family history on Ancestry.com.

But other parts of the family didn’t want anyone digging into the potentially salacious details of the past.

"People have a right to know who their parents and grandparents are," said Peter Harding, a retired psychiatrist. "I think that’s just a human right. There was a whole family that didn’t know for sure who their father and grandfather was. They deserved to know."

Peter Harding and James Blaesing connected and agreed to do a DNA test. When the results came back, Blaesing called Abigail Harding and greeted her by saying, "Hi, cousin." The families plan to hold a reunion and get better acquainted.

But it will take time for other family members to feel comfortable with the discovery.

Historians rank Harding low among the presidents, and he is known mostly for the Teapot Dome scandal that took place during his administration. Family members who researched Harding’s history said he was in a sexless marriage and had several mistresses.

Questions over Harding’s affairs and out-of-wedlock daughter have circulated for years. Visitors to the Harding home in Marion, Ohio, often ask whether he had a secret daughter. Tour guides have answered with a shrug and said there’s evidence it’s true.

James Robenalt, a historian who wrote about Harding’s affair with Phillips, said Harding’s legacy has been overshadowed by the allegations of affairs. The secrets were much more titillating when they were kept in the closet, he said. But now the family can heal and be reunited.

"Politically on a much, much bigger scale it is, I think, time for people to say ‘Ok, this happened, there’s no longer a mystery we have to solve,’" Robenalt said. "Let’s really look at Harding the politician, Harding the senator, Harding the president and really look at his record and try to assess it fairly."

Blaesing said that if his mother and grandmother were alive today, they would be pleased by the DNA findings.

"My grandmother — right now she has the biggest smile on her face," he said. "She is so happy that this is out there."

AncestryDNA spokesman Stephen Baloglu said the Harding story shows the power of DNA in rewriting history.

"The family connection is definitive," he said. "We were happy to help the Harding family members solve this longstanding family mystery."

In the Jefferson case, a DNA analysis published in 1998 found evidence that a member of the Jefferson family fathered at least one of Hemings’ six children.

On the basis of that and documentary evidence — namely, the whereabouts of Jefferson’s male relatives at the time — historians have generally agreed that Jefferson and Hemings had a sexual relationship, as had long been rumored.