Former Dark Angel star Jessica Alba was stunned when she had to kiss Bruce Willis for a scene in their hit movie Sin City - because he nervously tried to back out of doing it.

Alba, who plays a stripper in the movie, was ready to get intimate with the Die Hard hardman when he suddenly asked director Robert Rodriguez if they could approach the scene differently.

She says, "It was easy for me. I've done a few kisses in my day... We had this big romantic kiss and it was supposed to be like this big epic beautiful kiss... like you're anticipating this thing."

"We finally get to that scene and Bruce is sitting down and I'm going in for the kiss and he goes, 'Maybe I get up and walk away and she runs after me.' He says it to Robert when we were shooting it and Robert was like, 'What?'

"He got nervous - Bruce Willis! It was really cute, 'cause it's like this man, Die Hard and Moonlighting."

Willis was eventually forced to face his fears and pucker up for the kiss.

Alba adds, "It's a very romantic, passionate beautiful kiss."