AUSTIN, Texas -- Oprah Winfrey is confirming that Lance Armstrong came clean to her about his use of performance-enhancing drugs during their 21/2 hour interview Monday. She says the cyclist was "forthcoming" as she asked him in detail about doping allegations that followed him throughout his seven Tour de France victories.

Speaking on "CBS This Morning," Winfrey said she had not planned to address Armstrong's confession before the interview aired on her OWN network but, "by the time I left Austin and landed in Chicago, you all had already confirmed it."

Winfrey interviewed Armstrong at a hotel in downtown Austin. The session was to be broadcast on Thursday but Winfrey said it will now run in two parts over two nights because there is so much material.

Armstrong won every Tour from 1999 to 2005, but each of those titles was stripped last year as the U.S. Anti-Doping Agency released a massive report built around the testimony of former teammates. USADA accused Armstrong of masterminding a long-running and sophisticated doping operation on his teams.

The 41-year-old Armstrong vehemently denied the charges for years, and fiercely attacked his critics. But after losing his titles and being abandoned by corporate sponsors, he has changed course.