Ashton Kutcher found it "difficult" to like Bruce Willis because he used to sleep with his wife.

The 'Killers' star admits he initially found it challenging to get along with his spouse Demi Moore's former husband, because he couldn't stop thinking about how they used to have sex together.

He said: "At first it was difficult. You think, 'He's the guy who used to sleep with my wife', but once you overcome the jealousy, which is just your own personal insecurity, it gets easier."

The two men now get along brilliantly, and often spend time "hanging out" together with Demi and Bruce's daughters - and Ashton's step-daughters - Rumer, 21, Scout, 18, and 16-year-old Tallulah Belle..

He explained to Live magazine: "People ask us, 'How do you guys get on so well?' Well, I don't like everything Bruce does, and I'm sure he doesn't think everything I do is great. But being with Bruce is normal to me now. We go scuba-diving, skiing, we hang out with the girls together, we watch movies, we talk about sport."

Ashton and Demi made headlines when they first started dating in 2003, because the actress is 15 years older than the movie star hunk.

The 32-year-old star admits their relationship came as a shock to him too, but believes "fate" stepped in.

He explained: "I'd sworn off relationships before I met my wife.

"We met in New York, where I was hosting TV show 'Saturday Night Live', and at the time I was saying to myself, 'I'm going to party, I'm going to sleep with this girl and that girl and just have a good time.' And then I met Demi and it was like, 'I can't not be with this person.' I think it's fate in a way. Anyone who's looking for a relationship can't find one, but as soon as you let go of the need or desire, it'll show up, just like that."