London: 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.
"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," Heigl said.
"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," she added.
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," Luketic said.