“It was really weird,” he begins. “I’d just done eight months in South Africa. I came to England and the day I came back I had to do reshoots on ‘Thor 2.’” He raises an eyebrow. “And in the actual scene my hair was different, my … ” He stops and gives an exasperated sigh. “I was like, ‘This is torture, man. I don’t want to do this.’ My agent said: ‘You have to, it’s part of the deal.’ ”

In the scene in question in the superhero movie, “I’m actually falling down from a spaceship, so they had to put me in harness in this green-screen studio. And in between takes I was stuck there, fake hair stuck on to my head with glue, this f—— helmet, while they reset. And I’m thinking: ‘24 hours ago, I was Mandela.’ When I walked into the set the extras called me Madiba. I was literally walking in this man’s boots. [Within] six months, the crew, we were all so in love with this film we had made. I was him. I was Mandela, practically,” he insists.

“Then there I was, in this stupid harness, with this wig and this sword and these contact lenses. It ripped my heart out.”