Alex Pettyfer was worried he would "ruin" 'I Am Number Four'.

The blonde hunk - who stars as alien John Smith in the sci-fi fantasy film - was so concerned the film would not work with him in it he walked out of The Audition, before realising he would relish the challenge to play such an unusual part.

He told BANG Showbiz: "I find John so layered and so complex and such an interesting guy. He's from a different planet who comes to earth and has the same emotions as us and this vulnerability and is a reluctant hero and I just didn't know if people would believe that I was that guy.

"I didn't want to ruin the movie for anyone. And then I realised I didn't want to miss the opportunity of a lifetime and I realised this character was a challenge. Every actor looks for a challenge and so I thought I'll knock on the door and hope and pray that they'd let me back in and thankfully they gave me a second chance."

Once he got into the character, the actor relished the chance to play a person with superpowers.

He said: "There's this element of kid in everyone where we play out in the back garden and pretend to be Batman or Superman or Spider-Man, and why not do it for three months and pretend For Real, kind of. I think everyone wants to feel superhuman, some way or another and why not do it with lights coming out your hands."