When it comes to It Ends With Us, Colleen Hoover is where it all began.

Which is why it’s only fitting that the author of the novel feature in the film adaptation, which stars Blake Lively, Brandon Sklenar and Justin Baldoni, the latter of whom also directed the project.

“I do make a cameo in the movie,” Colleen revealed in an exclusive interview with E! News. “And it was a tough day. All I did was stand there and pretend to be talking in a party scene, but just know that took like 12 hours to film. It was insane.”

But don’t expect the best-selling author to be switching careers any time soon.

“I love knowing a little bit behind the scenes,” she noted. “But 12 hours of just reshooting that scene, I don't know how actors do it. After doing one day of pretending to act—it’s one of the hardest jobs in the world.”

It’s why as she thinks about her future book-to-film adaptations—her novel Verity is already in pre-production—she has one stipulation for her possible cameos.

As she joked, “I think I'll continue to choose non-speaking roles.”

Someone she was more than happy to take center stage, however, was Blake. While the film version aged-up protagonist Lily Bloom, Colleen said the choice allowed the perfect candidate to play the part.

“Blake has always been one of my favorite actresses,” she explained. “When they called me and told me, I didn't want to get my hopes up because I was so excited about the possibility of her playing this role. So when it actually happened and she showed up to set and started filming, it was just it was so surreal.”

The author also revealed Blake had a secret weapon when it came to this role: the sense of humor she and husband Ryan Reynolds put on display IRL.

“She is phenomenal.” Colleen continued. “The humor that you see between her and Ryan online, she brings so much of that to the character and with the subject matter and the emotions of this book, it needs that comedic levity. And she does it so well.”

And, she added, Blake had the perfect onscreen counterpart in costar Brandon, who plays Lily’s love interest Atlas Corrigan.

“When I heard that Brandon was playing Atlas,” she explained, “I was like,’ Oh, my gosh, he's gonna be so perfect. That kind of quiet, serious guy.’ And he brings that kindness and protectiveness to that role so well.”

She continued, “After watching the movie, and writing these roles, I feel like the casting is so spot on and everything I was hoping this movie would turn out to be.”

So don’t miss It Ends With Us, playing now in theaters.

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