With a day to go before the world learns exactly what Lance Armstrong said to Oprah Winfrey about his involvement in doping as a professional cyclist, the cancer charity he founded urged the fallen star to come clean.

"We expect Lance to be completely truthful and forthcoming in his interview and with all of us in the cancer community," Livestrong said in a statement released Wednesday. "We expect we will have more to say at that time."

The U.S. Anti-Doping Agency accused Armstrong in October of involvement in a sophisticated doping program while he was a professional cyclist. The world governing body for cycling, the International Cycling Union, stripped Armstrong of his seven Tour de France titles following the report. He's also been banned from the sport for life.

Speaking with her close friend Gayle King on "CBS This Morning" on Tuesday, Winfrey appeared to confirm media reports that the former Tour de France champion acknowledged to her that he had used performance-enhancing substances.

Winfrey's 2½-hour interview with Armstrong is to be aired Thursday and Friday on Winfrey's OWN cable network and on the Internet.

If true, such an admission would be a stunning reversal after years of vigorous denials, including lawsuits filed against accusers.

But it still will not be enough to reverse the lifetime ban and other sanctions that have kept him from participating in some triathlons -- the three-event sport he took up after retiring from cycling.

"Only when Mr. Armstrong makes a full confession under oath -- and tells the anti-doping authorities all he knows about doping activities -- can any legal and proper process for him to seek any reopening or reconsideration of his lifetime ban commence," said David Howman, director general of the World Anti-Doping Agency.

Winfrey said her team and Armstrong's camp had originally agreed not to leak details of the interview, and that she was surprised to find that not long after the interview, news reports were saying part of what Armstrong told her had "already been confirmed."

Winfrey declined to characterize Armstrong's answers or offer preview quotes, but said Armstrong came ready.

She said the former cyclist was forthcoming in what she described as an exhausting and intense interview taped Monday in Armstrong's hometown of Austin, Texas.

"We were mesmerized and riveted by some of his answers," she told CBS.

While the interview was revealing, Winfrey said, his demeanor surprised her. "He did not come clean in the manner that I expected," she said without elaborating.

Asked whether she thought it was difficult for him to "come clean" to her, Winfrey responded, "Yes. I think the entire interview was difficult."

It was not immediately clear why Armstrong apparently chose to acknowledge doping after years of denials.

Juliet Macur, the New York Times reporter who broke the news on January 4 that Armstrong was considering an admission of doping, said the athlete is too driven to accept life without sports.

"He has had (several months) to think about how he is lonely, how he doesn't have the adulation of fans at the finish line and nobody to beat right now," she said. "And it's driving him nuts."

Armstrong has been seeking to participate in triathlons sanctioned by U.S. Olympic authorities. Armstrong excelled at triathlons as a teenager and went back to the sport after retiring from cycling. He has been banned from officially sanctioned events.

Paul Willerton, who raced with Armstrong in the early 1990s, said any confession would be "just a starting point" for the cycling star.

"There are a lot of people still lying," Willerton said, naming former Armstrong consultant Dr. Michele Ferrari, and Johan Bruyneel, the onetime director of Armstrong's U.S. Postal Service team. "These guys are still perpetrating the lies and deception that Lance ruled over, and Lance holds the keys. He wants his control back, and he desperately wants to be liked by the American public. And you can't have it all."

The USADA suspended Ferrari for life in July, naming him as part of a large-scale doping conspiracy. Bruyneel is battling similar charges by the agency and said in October that he was "stunned" that its findings on Armstrong revealed details of the allegations against him.

Livestrong is also a consideration.

In October, Armstrong resigned as chairman of the charity he founded "to spare the foundation any negative effects as a result of controversy surrounding my cycling career," according to a statement posted to the group's website at the time. A few weeks later, he left the board entirely amid concerns that his involvement was harming the charity.

On Monday, he visited the charity and "expressed his regret for the stress the team suffered in recent years as a result of the controversy surrounding his cycling career," the organization said in a statement.

"Inspired by the people with cancer whom we serve, we feel confident and optimistic about the Foundation's future and welcome an end to speculation," the group said.