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Former presidential hopeful John Edwards admitted to an affair Friday with his former videographer, Rielle Hunter, though he firmly denied tabloid reports that he is the father of her child.

Edwards released a statement late in the day saying he made a "serious error in judgment," after telling ABC News' Nightline that he repeatedly lied about the affair during his failed presidential campaign.

"I made a serious error in judgment and conducted myself in a way that was disloyal to my family and to my core beliefs," Edwards said in his statement. "I was and am ashamed of my conduct and choices, and I had hoped that it would never become public.

"In the course of several campaigns, I started to believe that I was special and became increasingly egocentric and narcissistic. If you want to beat me up — feel free. You cannot beat me up more than I have already beaten up myself," he said.

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RAW DATA: John Edwards' Statement on His Affair

Edwards told ABC News that his wife Elizabeth, who has been diagnosed with an incurable form of cancer, learned of the affair in 2006, as did others in his family. He said the cancer was in remission when the affair began.

He told ABC News that he didn't love Hunter, 42, and knew he wasn't the father of her child because of the timing of the baby's birth on Feb. 27.

He said in his written statement he is willing to take "any test necessary" to prove he is not the father.

The National Enquirer first reported the allegations in October and published a new report in July on an incident between the tabloid's reporters and Edwards at a Beverly Hills hotel where Hunter and her child reportedly were staying.

FOXNews.com confirmed Edwards did have an encounter with reporters at the hotel and had to be escorted out. Edwards denied the allegations when they first flared late last year. But in recent weeks he and his inner circle have clammed up — he refused to respond to questions from FOXNews.com on the matter last month.

Edwards told ABC News Friday that he did visit Hunter at the Beverly Hilton, without first telling his wife, but that he only did so to keep her from going public.

Edwards said in his statement the only reason he denied the reports of the affair is because they contained "many falsities."

"But being 99 percent honest is no longer enough," he said.

Elizabeth Edwards, in a blog post on the liberal Daily Kos site, to which she occasionally has contributed in the past, Edwards spoke about her husband's affair Friday, adding she had learned about it in 2006.

"John made a terrible mistake in 2006," she writes. "The fact that it is a mistake that many others have made before him did not make it any easier for me to hear when he told me what he had done. But he did tell me. And we began a long and painful process in 2006, a process oddly made somewhat easier with my diagnosis in March of 2007."

She vowed his family would stand by his side.

"Our family has been through a lot. Some caused by nature, some caused by human weakness, and some — most recently — caused by the desire for sensationalism and profit without any regard for the human consequences. None of these has been easy. But we have stood with one another through them all. Although John believes he should stand alone and take the consequences of his action now, when the door closes behind him, he has his family waiting for him."

Click here to read the full blog post.

John Edwards denied to ABC News paying any money to Hunter to keep her quiet on the affair, but said his supporters could have done such a thing without him knowing.

A source close to Edwards' former campaign confirmed to FOX News that Fred Baron, a Dallas lawyer and former campaign finance chairman for Edwards, secretly provided financial help to both Hunter and Andrew Young, the former campaign aide reportedly claiming to be the father, with his own private funds.

Baron told The Dallas Morning News he paid relocation and housing expenses for Hunter to move from North Carolina to another location.He said Edwards did not know about the arrangement.

Edwards' political action committee did pay Hunter's Midline Groove Productions company $114,000 between 2006 and 2007 to produce a set of Web documentaries on Edwards.

But there are remaining questions over the identity of the father, despite the reported claims by Young.

No father is listed for the child in birth records obtained by FOXNews.com. And recently released tabloid photos appear to show Edwards holding a child at the hotel where he is alleged to have met with Hunter.

Edwards questioned the authenticiy of the photos. National Enquirer Editor David Perel told FOX News the tabloid stands by its claim that Edwards is the father.

“We absolutely believe the child is his," he said, challenging the former senator to take a DNA test.

"We'll publish the results no matter what they are," he said.

The admission Friday all but ends the speculation about his immediate role in the campaign of Barack Obama. Edwards, who dropped out of the presidential race in January, had been previously talked about as a potential vice presidential pick, or a cabinet member. But even his possible role as a speaker at the Democratic National Convention later this month was in doubt as the rumors of the affair continued to fester without a direct rebuttal.

"I think it's safe to say that John Edwards probably will not have a speaking role at the convention," political analyst Mary Anne Marsh said. "And whether he attends remains to be seen."

Edwards was a top contender for the Democratic nomination for president, pursuing his party's top spot — with his wife's support — even after announcing in March 2007 that her breast cancer had spread. Elizabeth Edwards revealed in November 2004, shortly after her husband and John Kerry lost the White House race, that she had been diagnosed with breast cancer. After months of remission, the couple announced the recurrence of the cancer 2 1/2 years later.

The former North Carolina senator was the Democratic nominee for vice president in 2004.

The Edwardses have three children — Cate, Jack and Emma Claire. Another son, Wade, died at age 16 in a 1996 car accident.

David Bonior, Edwards' campaign manager for his 2008 presidential bid, said Friday he was disappointed and angry after hearing about Edwards' confession.

"Thousands of friends of the senators and his supporters have put their faith and confidence in him and he's let them down," said Bonior, a former congressman from Michigan. "They've been betrayed by his action."

Asked at an Obama event in Nevada about the affair, Hillary Clinton said: "My thoughts and prayers are with the Edwards family and that's all I have to say."

The Associated Press contributed to this report.