"I would say he didn't come clean in the manner I expected," says Winfrey
Credit: George Burns/Harpo Studios, Inc

After being stripped of his seven Tour de France titles last August – and apparently lying in interviews for more than a decade – Lance Armstrong has admitted to using performance-enhancing drugs to win his multiple cycling championships, CBS News confirmed.

Armstrong, 41, made the personal confession to Oprah Winfrey in an interview to air over two nights starting Thursday on her OWN network, Winfrey announced Tuesday morning.

Appearing on CBS This Morning in what was basically a tease for her interview, Winfrey called her sit-down with the disgraced athlete “the biggest interview I’ve ever done,” adding, “I would say he didn’t come clean in the manner I expected.”

She did say, however, she “was satisfied” and “riveted by some of his answers” to her 112 prepared questions.

Winfrey offered no specifics of what he said, other than to say that after about 90 minutes, while they were taking a break, Armstrong asked her, “Will there be a point where you lighten up?”

Asked by This Morning‘s Charlie Rose if she found Armstrong “contrite,” Winfrey did say he was “forthcoming,” but “I choose not to characterize. I would prefer people make their own decisions.”

She did admit he was “truthful, serious [and] certainly had prepared himself for this moment.”

As for “why now,” Winfrey said, “He was just ready,” and she cited the mounting pressure upon Armstrong in the past weeks, which had “just increased in intensity.”

Immediately following her interview with Armstrong, which took place Monday at the Austin, Texas, Four Season Hotel, Winfrey Tweeted: “Just wrapped with @lancearmstrong More than 2 1/2 hours . He came READY!” On CBS This Morning, she said he came with a small group of people, but “we did not allow the lawyers in the room.”

The interview reportedly followed Armstrong’s appearance at his Livestrong cancer charity offices in Austin, where he was said to have apologized to the 100 people on the staff.

There are also reports that Armstrong is in talks to return a portion of the millions of dollars in taxpayer money received by his former team, U.S. Postal Service, and that he may be willing to name others who used performance-enhancers.

In addition, CBS News reports that senior Justice Department officials have suggested that the government join a lawsuit filed by a former Postal Team member accusing Armstrong of defrauding the federal government.