British actor Jamie Campbell Bower was dismayed by the negative reaction he received from fans when he was cast in upcoming fantasy blockbuster The Mortal Instruments: City Of Bones.

The Harry Potter star landed the role of Jace Wayland opposite his rumoured girlfriend Lily Collins in the first film adaptation of Cassandra Clare's young adult book series The Mortal Instruments.

Bower was delighted to land the job, but admits his excitement was marred by a fiercely negative reaction from fans of the novels who didn't agree with his casting.

He tells Britain's GQ magazine, "I'd be lying if I said the reaction wasn't negative. People have preconceived notions of who the character should be. And then there's someone like me who changes that.

"(They say) 'He's too ugly' or 'He's not butch enough' or 'He doesn't work out enough'."

However, Bower is adamant the criticism was unfair because it was levelled at him months before filming began and before he had time to get in shape for his role of the film's muscular hero.

He adds, "All this s**t, basically, that means f**k all. Because, you know, I'm a product, effectively. I'm more than happy to change, and put the time and effort in. You know, we weren't shooting for another six months."

The Mortal Instruments: City of Bones is due for release in the U.S. in August (13).