'Mortal Instruments' Cast on 'Twilight'-Size Fame

'Mortal Instruments' Cast on 'Twilight'-Size Fame

Are Lily Collins, Jamie Campbell Bower and Kevin Zeger ready for a lifetime of tabloid features, screaming fans and paparazzi? Not really, but The Mortal Instruments threesome tells ET they're strong enough to stay sane through the ups and downs of superstardom, should it happen.

"This isn't any of ours' first movie," explains Bower, who is tasked to play heartthrob Jace Wayland in the popular series' big-screen adaptation. "If [the film] does well, it does well. Does that mean that it's going to change who we are as people? No. I'm still going to be Jamie from London. I'm still going to do what I want to do and hang out with my mates. Nothing's going to stop me from doing that."

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Castmate Kevin Zegers, who portrays Mortal Instruments' gay fan-favorite Alec Lightwood in the flick, adds, "I think we all have that checks and balance thing, which is good, and I think you need it because [fame isn't] something you can adjust to unless you're dealing with it at the same time."

Co-star Lily Collins agrees, telling ET that she's gained enough trust with her film family to "call people out," which she believes will keep the close-knit cast from going off the rails if (or when) they encounter the perils of fame.

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Based on Cassandra Clare's adult fantasy novels, The Mortal Instruments: City of Bones follows teenage girl Clary Fray (Collins), who sets on a quest to rescue her mother from a demon that took her from their home in New York City. In the course of her search, her life is forever changed by the family secrets she uncovers.

The action-adventure movie opens August 21.