AceShowbiz - Ashton Kutcher impressed his "Killers" co-star Katherine Heigl with his down-to-earth attitude - because he was "really nervous" about stripping off for a scene. The actor plays an undercover assassin who quits his job when he falls in love with a woman played by Heigl and spent weeks honing his physique before filming.

But Kutcher was still worried about appearing topless on-set - a trait Heigl found endearing. She tells Britain's Live from Studio Five, "Ashton spent that entire day worried about how he looked on camera, like anybody would, because he knew he'd be shirtless for that whole entire scene."

"He worked hard and he was really nervous going, 'Do I look alright, do you think I look okay?' It was really endearing and charming! And director Robert Luketic admits he was shocked by Kutcher's workout regime: "He arrived in France and walked in and took his shirt off and said, 'Is this built up enough?' and I said, 'Who's your trainer?' and he said, 'I did it from one of those DVDs you buy on late night television.' He was serious - he didn't have a trainer."