Gerard Butler felt "burned out" after filming 'Machine Gun Preacher'.

The '300' actor was "exhausted" when he finished recording the biopic - which tells the story of former drug-dealing biker Sam Childers, who found God and became a preacher to Sudanese orphans who had been forced to become soldiers - because he had to do gruesome research to prepare for the project.

He said: "I've seen footage of people being hacked to death. Usually when you finish a movie there's this period of adjustment, but you come out of it with some buoyancy and excitement. Whereas with this, I felt burned out and exhausted."

The 41-year-old star felt "haunted" after filming the movie, but he felt much better following a trip to Sir Richard Branson's safari lodge, where he was able to take in the animals and "restorative power" of being in the wild.

He told Seven magazine: "I'd brought some friends down to South Africa, where we'd been filming, and we were supposed to be going on safari, but I actually felt haunted, like, why would I want to be with people and look at animals?

"But the strange thing was, I did go to Richard Branson's safari lodge, actually, and I've got to say that the restorative power of being out in the wilds, standing five feet from an elephant walking past with her young, really did the trick."