Reporters at a recent press conference in Spain were nothing but stunned when actor Colin Farrell appeared at the event looking shockingly thin.

Why the major transformation for this Hollywood bad boy?

"I lost weight because my role demanded it," said the 31-year-old of his upcoming film, Triage. "It was all very healthy."

It was a few sentences from the Scott Anderson novel that inspired Farrell's drastic slim-down: He went to the bathroom to shave. Once his beard was gone he saw that his face had become drawn. He pressed at the hollows beneath his eyes, the pronounced nubs of his cheekbones.

Farrell, not willing to fess up to his weight-loss secrets, plays a war reporter in Bosnia in this new film and spent five weeks perfecting his character.