Sienna Miller was left 'shaking with tears' after a nine-hour sex scene with Ben Affleck

They star as lovers in upcoming gangster flick Live By Night and at one point, Sienna Miller and Ben Affleck spent nine hours filming sex scenes.

Appearing at the premiere for the Affleck-directed film, in which she plays Irish minx Emma Gould, Miller told E! about their many sex scenes, revealing they left her in tears - of laughter.

Sienna Miller in a scene from the film, Live By Night. Photo / AP

Live By Night is an action-packed movie, but one which wouldn't be complete without a romantic story, for which Sienna admitted the duo were forced into a bevy of romantic scenes, the Daily Mail reports.

She said: "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.

Sienna admitted their whopping nine hours of sex scenes tickled her.

"In that environment, it was a cool scene. 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?'

"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."