Often ranked as one of the least successful U.S. presidents, Warren Gamaliel Harding was the 29th President of the United States, from 1921 to 1923.

Warren G. Harding III knows full well what advice he'd give to Sen. Ted Kennedy concerning allegations by a Vancouver man claiming to be the love child of the late U.S. president John F. Kennedy.

Ignore both the man and his story.

"Even doing DNA testing won't change it," said Harding, a grand-nephew of former U.S. president Warren G. Harding. "People will always believe what they want to believe.

"If you do the test, and it shows he's not the president's son, people will say, 'Where did you get the DNA? What about the chain of custody of the test?' There's always going to be somebody who makes the claim. I think it's just something (any presidential family) just have to accept in a certain way."

Harding, 66, a doctor specializing in sports medicine in Cincinnati, brings a unique perspective to the sensational claims made in recent days by Jack Worthington, 46. The B.C. man claims his mother was one of Kennedy's lovers and he is the product of that affair.

Harding's own presidential family has been fighting - and losing according to some historians - similar allegations since the 1920s.

Warren G. Harding, a former newspaper publisher in small town Ohio and later a Republican U.S. senator, was elected president in 1920. Like Kennedy, he only served two-and-a-half years in the White House, dying from heart trouble shortly after visiting Vancouver during the summer of 1923.

Greatly beloved at the time, his legacy was in tatters in less than a decade, largely due to the allegations of Nan Britton. She claimed that she and Harding carried on a lengthy affair that included sex in the White House - decades before Monica Lewinsky became a White House intern - that resulted in her giving birth to a baby girl, Elizabeth Ann. Her 1927 book, The President's Daughter, considered pornography by some authorities and suppressed, was privately published and sold upwards of 100,000 copies.

According to Britton, their physical love affair began when she was a virgin barely out of her teens.

"Mr. Harding (who was married) confessed to me that he had never possessed a woman who had hitherto been possessed of no man, and perhaps that fact concerning me made me the more desirable to him, in addition to his love for me," she wrote.

She claimed they first had sex in a New York Hotel on July 30, 1917 when she was 20. Britton wrote she and the senator, still naked, were raided by the vice squad.

Their child was conceived in the U.S. Senate itself in January 1919, she claimed.

"Mr. Harding told me he liked to have me be with him in his office, for then the place held precious memories and he could visualize me there during the hours he worked alone," she wrote. "Mr. Harding was careless of consequences, feeling sure he was not now going to become a father."

She said that the former president never met his daughter but did provide some form of support while he was still alive. Historians in the U.S. still debate whether her story is true.

The younger Harding strongly denies his famous relative had any children at all.

His grandfather, also a doctor, met Britton after his president-brother's death and was convinced beyond any doubt that the woman's story was false. His grandfather's word, coupled with his medical training and experience, is good enough for him, he said.

Nan Britton, maintaining her love for Harding until the end, was 95 when she died in 1991.

As for Elizabeth Ann, she married, had her own family (living under the name of Blaesing) and ended up in Oregon, where she died in 2005 at age 85. She always believed she was Harding's daughter but refused to discuss her possible parentage.

At St. Bonaventure University history professor Dr. Phillip Payne, the author of the forthcoming Dead Last: The Public Memory of Warren G. Harding's Scandalous Legacy, says he disagrees with Harding's advice to Kennedy.

"If the Kennedys can put the (Vancouver) story to rest they should," he told Sun Media. "Once people start to speculate then the speculations become part of the legacy people will be attached to, especially in popular culture ... Something fills that (historical) void and what fills that void is speculation and innuendo."

Payne says that Harding's presidency today is judged solely on the claims of Nan Britton by most rather than on its accomplishments. And even Harding-era scandals such as the Teapot Dome affair - that have occupied the few historians that have studied the former president - are overshadowed by Britton's story.

"It (a presidential love affair) is not complicated to understand by the public like (the) oil leases (involved in Teapot Dome)," he said.