Zac Efron taken aback by Nicole Kidman's improvised dancing

Zac Efron was left squirming in his underwear when Nicole Kidman caught him off guard by asking him to dance during their shoot for The Paperboy.

The actor was bracing himself to deliver an emotional scene in the erotic thriller, and was stunned when his co-star suggested they dance while he was wearing nothing but a pair of tight, white briefs.

However, Efron admits sharing a dance with the actress in the rain was a career highlight.

He tells talk show host Ellen DeGeneres, "Nicole is so amazing to work with but she's also very improvisational and once she finds the character she can sort of manoeuvre in and out of the lines. You never know what to expect.

"This was supposed to be a very serious scene. It was sort of an intense dramatic moment for me. So I was very prepared to give my all in a dramatic moment and before I knew it music starts to turn up around me and she kind of looks at me and says, 'Do you want to dance?' And they're still rolling so I can't really say cut! And before I knew it we were improvising an entire dance in the rain. It's one of my favourite scenes in the movie. That is one of the coolest things I've ever done. It is the day I think I became a man."