Lance Armstrong has revealed that leaving his Livestrong Foundation "hurt like hell".

The 41-year-old American cyclist was forced to step down from his role as the chairman of the cancer-fighting charity he himself founded in October last year following allegations of drug abuse.

"The one person I didn't think would [drop me] was the [Livestrong] Foundation," Armstrong told Oprah Winfrey in an interview when asked what his most humbling moment was. "That was the most humbling moment.

"To get that call - two parts. One, step down as chairman but stay on the board, stay involved. That wasn't enough. For the people, our supporters, and then a couple weeks later the next call came. And 'we need you to step aside'.

"I don't think it was 'we need you to step down', it was 'we need you to consider stepping down for yourself'. I had to think about that a lot. The Foundation is like my sixth child and to make that decision to step aside was... that was big.

"I was aware of the pressure. I wouldn't say forced out. I had interactions with some of the board members. It was the best thing for the organisation but it hurt like hell. That was the lowest."

Armstrong admitted on Thursday that he took performance-enhancing drugs during his cycling career.