Ridley Scott's got your back when it comes to your behind.

The Oscar-nominated director’s historical epic “Napoleon,” starring Joaquin Phoenix as Napoleon Bonaparte and Vanessa Kirby as wife Josephine, is in theaters now with a 2½-hour runtime. Scott's also prepping an extended cut with about an extra hour of material that will stream on Apple TV+ next year but “would be too fat for cinema,” he says.

The film that's out currently “is my judgment on what I call the 'bum ache factor,’ ” he explains. “When an audience is sitting there, there's a moment where they go, ‘Jesus, is it going be an hour and a half before we have that Japanese dinner? I'm exhausted.' You don't want that to happen.

“Every scene should be a part of an engine of the overall play. If it isn't, chances are it shouldn't be there.”

A couple of Kirby’s favorite scenes were edited out of the theatrical version, including an assassination attempt on Napoleon. “That was a really incredible day filming in her life,” Kirby says.

One important sequence that Scott says is “absolutely” going into the extended cut finds Josephine in prison during the Reign of Terror – she was arrested soon after her first husband, who was later beheaded – and choosing to cut off her hair.

“The hair was cut because hair down the back of the neck could stop a (guillotine) blade,” Scott says. “The women cut their hair because they just wanted one shot of losing their head and that's it. They didn't want to have three goes at losing your head.”

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In the theatrical cut, Josephine is first seen right after getting out of jail in Paris, sporting a pixie cut, before meeting her future spouse (and eventual French emperor).

“I really learned, when I read about that part of her life, how much of a survivor she is and how close she came to death,” says Kirby, who recommends Kate Williams’ biography “Josephine: Desire, Ambition, Napoleon” for further historical background. “She really was a day away from being killed. I can only imagine that you would commit so much more intensely to life, which I think is why she ended up as empress. I feel like that was a big, huge part of changing her, the nature of her personality and her ability to adapt.”

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