AP
Relatives of Harding and Britton submitted DNA to AncestryDNA, a division of Ancestry.com, and the results proved that Britton's daughter, Elizabeth Ann Blaesing, was Harding's love child.
"We're looking at the genetic scene to see if Warren Harding and Nan Britton had a baby together and all these signs are pointing to yes," Stephen Baloglu, an executive at Ancestry, told the Times.
"The technology that we're using is at a level of specificity that there's no need to do more DNA testing. This is the definitive answer."
The affair was a major scandal of the day - Britton published a tell-all book, "The President's Daughter," four years after Harding died.
The memoir became an "instant bestseller," according to a Times article from 1998, as it predated the Monica Lewinsky scandal by decades and marked the first time that the mistress of a US president wrote a book detailing her affair with America's leader.
Harding was rumored to have several mistresses, but Britton was still skewered in the press for claiming she had an affair with the president.
Britton grew up in Marion, Ohio, where Harding was a newspaper publisher. Britton's father reportedly knew Harding and Harding's sister was one of Britton's teachers. She admired Harding from afar until she asked for his help finding a job and he agreed to meet with her in New York, according to the Times. She was 31 years younger than him.
She claimed the affair lasted more than six years and that the two met in various places, including Harding's office in the Senate and a closet in the West Wing.
Harding reportedly supported his daughter financially but did not acknowledge the child as his publicly. The two never met.
Harding died in office in 1923. Britton went public with the affair after she realized the financial support would dry up.
After Britton made the affair allegations, the Harding family "really vilified" Britton, according to Peter Harding, a grandnephew of the president.
"My father said this couldn't have happened because President Harding had mumps as a kid and was infertile," he told the Times.
Although Britton reportedly destroyed the letters she and Harding sent each other, the letters Harding sent to another mistress, Carrie Fulton Phillips, have been published online by the Library of Congress.
He wrote her poems:
Library of Congress
And created code words for their correspondence:
Library of Congress
Their affair reportedly lasted from 1905 until 1920, according to the Library of Congress, meaning he likely had several mistresses at once.
Harding was married to his wife, Florence, from 1891 until he died.
Some Harding family members seem willing to accept the DNA evidence of the late president's love child, but others still aren't so sure.
Richard Harding, 69, another grandnephew of the president, told the Times that the love child rumor is "still to be proven" but that he'd welcome the new family members if he saw enough evidence supporting the claim.
He said of the Britton relatives: "I hope they'll find their new place in history is meaningful and productive for them."