Lily Collins has said her upcoming film, The Mortal Instruments: City of Bones, is "sexier" than other young adult book adaptations.

Speaking to The Hollywood Reporter at Comic-Con, the actress said of the film, which she stars in alongside Irish actor Robert Sheehan: "It's really dark. There's humour in it, which I think makes it different than any other franchise."

Collins continued: "It has a comedic undertone. But the world is darker than some of the teenage franchises that we've seen. It's very goth and underground.

"So, probably not for the youngest viewers. I think it will appeal to them because [of] the boys having their action sequences, but I definitely think it will appeal to the older groups because it's sexier."

The actress, who was in Dublin recently shooting Cecilia Ahern's new film Love, Rosie, said that she is surprised by the level of fervour surrounding The Mortal Instruments: City of Bones, which is released on August 21.

She said: "It's exciting to see the excitement that people have about it. I was in Dublin recently shooting a movie in the middle of nowhere, and these girls just come over to me crying and they just started screaming, 'August 21!'. And I said, 'What happens on August 21?' I was totally in a different movie mindset. They're like, 'The movie!'"

Collins also opened up about her costumes on the film, saying: "It was awesome because Clary [her character] gets to go from being this normal teenage girl who dresses in boyfriend jeans and combat boots and leather jackets, and then all the action starts, and she wears tight leather pants, a dress that is basically a top it's so small and then five-inch thigh-high boots.

"I didn't practise any of my stunts in my costume. So all of a sudden, I'm thrown in to running up stairs and crawling at four in the morning in this outfit. But it was all worth it because I loved playing that badass, sexy, dominatrix-y fighter character."