The popstar confirmed to fans last night (28 July) that she will star alongside Joseph Gordon-Levitt in the sequel of the action thriller.
"It's true! I'll be in Sin City 2: A Dame to Kill For with my favourite scene partner Joseph Gordon-Levitt," Gaga wrote on Instagram. "I love [director Robert] Rodriguez he really killed this one!"
'Bad Romance' singer Gaga shared a photo of her character on Instagram, in which she plays a rather glamorous waitress.
She told a fan on Twitter: "It's not a big part but I'm always happy to do it! When I take a music break I'll have more time."
When one fan suggested she take up a lead movie role, Gaga replied: "I'm just warming up, I gotta wet my feet first. Plus I perform best when I have time to focus."
Sin City: A Dame to Kill For, which also stars Jessica Alba, Bruce Willis, Mickey Rourke and Rosario Dawson, is a follow-up to the 2005 hit Sin City based on Frank Miller's famous comics.
The movie hits US cinemas on August 22. UK screenings are expected to be announced at a later date.
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Watch Gaga's 'Applause' video below: