Dave Franco has revealed how he made the spontaneous decision to flash his bottom at Sienna Miller.

The 29-year-old actor mooned at the British actress in one scene in their new film, Unfinished Business, and joked she wasn’t too impressed with his cheeky move.

“That was not in the script. I think that was our last day filming in Berlin and at that point, we all felt pretty comfortable with each other and I decided, ‘Let’s show Sienna Miller my ass’, and there you have it,” he said.

Sienna in Unfinished Business (20th Century Fox UK)
Sienna in Unfinished Business (20th Century Fox UK)

The Bad Neighbours star continued: “She was on the other side of the glass. I just walked away after we were done with the scene, so I don’t think we had any interaction after that. It might have been our final interaction!”

Dave – the younger brother of actor and filmmaker James – said other takes failed to make the final cut.

“There were some more crude takes that we didn’t even use,” he said. “I did one where my ass was hanging out and I actually jumped up, and you might have seen something maybe kind of dangling. It was a little unuseable.

“So what you saw in the movie is the tame version of what we ended up shooting.”

Tom, Vince and Dave in the film (20th Century Fox UK)
Tom, Vince and Dave in the film (20th Century Fox UK)

Dave, who plays a businessman alongside Vince Vaughn and Tom Wilkinson, admitted a scene in a giant hamster wheel was quite stomach-churning.

“When we first got in the giant hamster ball, everyone was really jealous and wanted to get in there. It was really fun for the first 30 minutes but then, when you’re in that ball for ten hours rolling around, it makes you a little nauseous,” he said.

“That being said, we had a great time and the fact that rolling around in a hamster ball is part of my job, is a cool thing.”

Unfinished Business, which also stars Nick Frost and James Marsden, opens in UK cinemas on March 6.