Idris Elba has admitted he had moments of self-doubt about whether he could play Nelson Mandela.
The Wire actor stars as the former South African president in Mandela: Long Walk To Freedom, a part originally earmarked for Hollywood star Denzel Washington.
Idris said: "At some point the DNA changed and it didn't work for him to do the film, so my name was thrown in that mix. In actuality it was really easy to get the job, but I didn't believe that I had gotten it."
However, once the reality of landing the part set in, so did the 41-year-old's nerves.
"I was like, 'Damn, do I have this performance in me?'" confessed the actor. "Everyone knows what Mandela looks like and sounds like and I'm not like any of that. It was a massive challenge, but it was time to grow up and really put my acting chops out there."
Idris embraced the harsh realities of Mandela's life while he was making the film and revealed he also pushed his fellow actors to embrace uncomfortable realities too.
Talking about a day shooting scenes that focused on Mandela's 27 years in jail under white minority rule, the British star revealed he sensed that a couple of white actors were struggling to portray the brutality with which Mandela was treated.
"They felt bad. ... I could see it in their eyes. I spoke to director (Justin Chadwick) and I said, 'I need these guys to go back to their core. If there is any sense of racism in them I need them to bring it up. If there is a black person that they don't like let me hear it and feel it'," said the actor.
"That was important because it would come through in the performance and suddenly it becomes the biopic that's safe."
Mandela: Long Walk To Freedom - which also stars Naomie Harris - is released in cinemas on January 3, 2014.