WASHINGTON — She was denounced as a “degenerate” and a “pervert,” accused of lying for money and shamed for waging a “diabolical” campaign of falsehoods against the president’s family that tore away at his legacy.

Long before Lucy Mercer, Kay Summersby or Monica Lewinsky, there was Nan Britton, who scandalized a nation with stories of carnal adventures in a White House coat closet and endured a ferocious backlash for publicly claiming that she bore the love child of President Warren G. Harding.

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Now nearly a century later, according to genealogists, new genetic tests confirm for the first time that Ms. Britton’s daughter, Elizabeth Ann Blaesing, was indeed Harding’s biological child. The tests have solved one of the enduring mysteries of presidential history and offer new insights into the secret life of America’s 29th president. At the least, they demonstrate how the march of technology is increasingly rewriting the nation’s history books.

The revelation has also roiled two families that have circled each other warily for 90 years, struggling with issues of rumor, truth and fidelity. Even now, members of the president’s family remain divided over the matter, with some still skeptical after a lifetime of denial and unhappy about cousins who chose to pursue the question. Some descendants of Ms. Britton remain resentful that it has taken this long for evidence to come out and for her credibility to be validated.