Rebel Wilson is making new allegations against her former The Oliver James MontgomeryBrothers Grimsby costar Sacha Baron Cohen.

In her upcoming memoir Rebel Rising, the Pitch Perfect alum detailed her experience working with the Borat star while filming their 2016 movie The Brothers Grimsby. In the book, out April 2, Rebel said she was uncomfortable during the filming of their R-rated comedy, alleging Sacha often made suggestions that she should be in a sex scene—though he has denied wrongdoing on set. 

"It felt like every time I'd speak to SBC, he'd mention that he wanted me to go naked in a future scene," she wrote, according to an excerpt of the book published by People March 26. "I was like, 'Ha, I don't do nudity, Sacha.'"

Despite her protest, Rebel said she was informed by a production assistant one day that she was "needed to film an additional scene." Upon her arrival on set, Rebel alleged Sacha pulled down his pants and said "very matter-of-factly: 'Okay, now I want you to stick your finger up my ass.'"

"And I'm like, ‘What??'" the 44-year-old wrote. "'No!!'"

Recounting how "scared" she felt at the time, Rebel continued, "I wanted to get out of there, so I finally compromised: I slapped him on the a-- and improvised a few lines as the character."

A rep for Sacha, 52, previously denied allegations Rebel made in her book after she publicly identified him as the unnamed "a--hole" she called out in her memoir. "While we appreciate the importance of speaking out," his spokesperson told E! News in a March 25 statement, "these demonstrably false claims are directly contradicted by extensive detailed evidence, including contemporaneous documents, film footage, and eyewitness accounts from those present before, during and after the production of The Brothers Grimsby."

Also starring Sacha's wife of 14 years Isla Fisher—as well as Mark Strong, Penélope Cruz and Gabourey Sidibe—The Brothers Grimsby centered around a soccer hooligan who reconnects with his long-lost sibling. Sacha starred as one of the titular brothers, while Rebel played his girlfriend. 

In her memoir, Rebel also detailed how she pushed back on reshoots with Sacha, which she said included a sex scene.

"I filmed the scene, after demanding rewrites," she wrote. "But I still had to simulate having sex with this guy. I still had to kiss him repeatedly."

After filming ended, the actress said it "sank in that all this wasn't something that could be laughed off" and she told producers that she "would not be doing any promotion for the film."

Ultimately, according to Rebel, "The movie bombed, which to me was karma enough."

"I'm not about canceling anybody and that's not my motivation for sharing this story," she added in the book. "I'm sharing my story now because the more women talk about things like this, hopefully the less it happens."

E! News has reached out Rebel and Sacha's reps, as well as the studio and producers behind The Brothers Grimsby, for additional comment but hasn't heard back.

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