Lance Armstrong biopic The Program to close Austin Film Festival

But speaking to the BBC at the BFI London Film Festival, where the film had its European premiere, the actor said he felt the drugs had “definitely damaged” his body, even though he took them in a “contained, doctor-supervised manner”.

Foster recently disclosed that he took the drugs in an interview with The Guardian, though the actor declined to say which drugs he took or how long he took them.

Armstrong, once considered one of the greatest athletes of our time, earned seven consecutive Tour de France titles from 1999-2005.

Responding to media interest in that disclosure, he said: “I think it’s representative of this story: what takes off and what people are attracted to is not necessarily the real whole, entire story”. He added: “I think it’s a pretty decent film and I was hugely honoured to be involved in it. We always knew there was going to be a Lance Armstrong movie; we never knew it was going to be this particular movie”. As I recall Lance Armstrong did at least pretend to make it look hard and my guess is he wasn’t pretending, especially as the film implies that pretty much everyone else he was racing was doping too, and on the same dope.

Despite the toll it has taken on his body, Foster insists the decision to take the drugs was all his own, saying director Stephen Frears had no idea about it until after filming was complete. It deals with how, over the course of 13 years, Walsh doggedly maintained his investigation of the Texan who defeated cancer but, in superhuman and, ultimately, unbelievable terms, conquered the Alps and the world’s greatest bike race seven times over.

On Foster, he said: “He’s terrific”. There’s a running gag (of sorts) throughout The Program that they’re going to make a film of Armstrong’s life. “If we hadn’t got Ben we wouldn’t have a film”. She said: “Sometimes when you’re dealing with something quite controversial, you need to retain a level of impartiality in making the movie”. “And they will always be one step ahead”.

The Program will be released in the United Kingdom on Friday, and is set for a 2016 release in the US.