Paul Rudd nervous to ask Billie Joe Armstrong to appear in This Is 40

Actor Paul Rudd persuaded Billie Joe Armstrong to make a cameo appearance in his latest movie This Is 40 by calling the Green Day rocker personally to ask for the favour.

Rudd re-teamed with his Knocked Up co-star Leslie Mann and her director husband Judd Apatow for the follow-up film, in which he plays a music executive, and used his character's job as an excuse to get Armstrong involved in the project.

The actor admits he knows the singer socially, but felt nervous about offering him the part.

He tells the BBC, "I'm not good friends with the guy but I've become kind of friendly with him and I still can't believe it like, 'Oh my God, that's Billie Joe Armstrong'. I don't get used to that kind of thing.

"I knew that with music and what I'm doing in the movie (his character's job) and I thought, 'I'm gonna (going to) call him', and I asked Judd beforehand... And I got up the nerve to (pick up the phone) and he (Armstrong) said, 'Sure,' and that's how that happened.

"I kind of felt like, 'Wow, I can't believe that he said yes' and that felt kind of cool. "