Jamie Campbell Bower piles on the pounds for Mortal Instruments

Harry Potter star Jamie Campbell Bower is bulking up and hitting the gym as he prepares to play a demon fighter in upcoming fantasy blockbuster The Mortal Instruments.

The actor has been cast as Jace Wayland, a half-man, half-angel who romances Lily Collins in the forthcoming adaptation of the best-selling young adult novel.

And the 23 year old reveals he has embarked on a tough new exercise regime to ensure he is as fit as possible when shooting kicks off.

He tells Daily Telegraph, "I'm in physical training. I'm drinking lots of protein shakes. I go to the gym and do weights in the morning, in the afternoon I do Krav Maga, a martial art. If you live in a dodgy area like I do (in London), then it could be a handy thing to have."