It's always a little strange when a child actor grows up before moviegoers' eyes. They almost inevitably choose to navigate the choppy waters of adult stardom by taking on films that feature, well, sex. And while it might be uncomfortable for fans, "Harry Potter" co-star Rupert Grint thinks nothing could be more awkward than having to watch that first nude scene ... with his parents.

"Filming it was a really nerve-racking experience," Grint told the U.K.'s Mirror of the provocative scene from his movie "Cherrybomb." "But the worst bit was watching it with my parents," he admitted.

The 21-year-old actor was only 12 when he won the part of wizard Ron Weasley, after appearing in some plays staged by a local theater group. In "Cherrybomb," which is currently making the film-festival rounds, Grint plays Malachy, one of three teenagers out for a wild weekend of drugs, drinking, shoplifting and sex. Still, when it came time to watch the movie with the 'rents, the actor found himself in a hairy -- and emphatically un-"Harry"-- situation.

"It was agonizing," Grint said. "The scene's quite tastefully done, but it's not the sort of moment you really want to share with your mom and dad."

Grint said that even though he knew the racy part was coming, all that did was to add to his mounting anxiety. "When the scene arrived, we all sat there not really saying anything," he explained. "Afterwards, nobody talked about it -- which was kind of a relief."

The scene involves Grint and Kimberley Nixon, a 24-year-old British newcomer. "Shooting the sex scene was a pretty anxious time, because I didn't know how it would be shot," Grint said. "It's the anticipation that scares you most.

"I really didn't want my bum up there on the screen," Grint added. "But the scene isn't too graphic, and most of it is suggested rather than seen. But you do feel very self-conscious. It was more embarrassing for Kimberley, because a lot more of her body is shown. But you just have to get into that moment and get on with it."

For Grint fans not in the U.K., "Cherrybomb" is touring festivals, and U.S. release plans are yet to be determined.

What do you think of the "Harry Potter" actor moving into more adult movie roles? Tell us in the comments!

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