Bruce Willis was put off by how "weirdly" alike Joseph Gordon-Levitt was to him on the set of their new movie.

The pair star in Looper - a sci-fi action film based in a futuristic gangland. Bruce plays a future version of Joseph's character, and the action star was astounded by how well Joseph picked up his mannerisms.

"I was sitting across from Joe across a table. I was supposed to act and get all my lines right, but I just found myself looking at him and thinking how weird it was," he laughed to Flicksandbits.com. "It was an honour. "It's really a strange thing to see someone that looks like a young version of yourself. He's a great actor, I love his work and I just love what he did in this film, Looper. He picked up some of my cadence of speaking, which was odd, and yet, really cool at the same time.

Bruce found the concept strange at first, but soon adapted to the idea.

"It seems like an impossible task to try to act with someone who's supposed to be you, supposed to be the younger you. And at some point you have to let go of it and just believe that you're in the story, that you're part of the story," he said.