Any movie star will tell you that the most awkward and potentially embarrassing aspect of their job is filming sex scenes.

Trying to remain cool and professional in a cramped room, half-naked with your colleagues and in front of dozens of crew members, cameras and lights… enough to make even the steeliest of nerves falter.

However, Sienna Miller reckons there’s one way to cure this – if both actors approach it with a sense of humour. She was cast opposite Ben Affleck in Live By Night, playing the Irish moll Emma Gould to Affleck’s gangster Joe Coughlin, and spoke at the red carpet premiere about having to film sex scenes for a whole DAY.

Sienna MillerSienna Miller filmed an entire day of sex scenes with Ben Affleck

“There was a montage in the script saying we did it everywhere: in the car, in the bar… I was like, 'That's an entire day of just love scenes! OK. How do we do this?'” she remembered in an interview with E! News.

More: Jennifer Lawrence admits she had to get “really drunk” before sex scenes with Chris Pratt on ‘Passengers’

“Obviously, by the time nine hours of it has gone past, I was shaking with tears running down my face. I mean, I can't tell you — but you have to laugh. Ben is just professional. It is what it is.”

“It's hysterical,” Miller added. “Ben and I are like brother and sister, thank God, so there was no awkwardness. There was just a lot of stupid giggling. He's very professional — I am not, but he is. In that environment, it was a cool scene.”

Specifically she remembered an incident where Affleck, who also directed the film, told the cinematographer to “keep rolling” so they could film the same scene multiple times “without having to cut”. Initially, Miller was thrown, thinking that Affleck’s character was supposed to be some kind of love-making god.

“It turns out that he was just giving himself options without cutting,” she explained. “But to me it was the funniest thing. I was like, 'No one can do what you're doing, the marathon love scene’. There will be some outtakes from that [scene] where I have to walk out of the room, because I just have tears running down my face!”

More: What does ‘Live By Night’ actually mean? Ben Affleck explains…