Bradley Cooper and Suki Waterhouse

Bradley Cooper and Suki Waterhouse

Bradley Cooper has gained 40 pounds for his upcoming movie.

The 39-year-old actor has bulked up in the gym to play late real-life Navy SEAL Chris Kyle in the Clint Eastwood-directed film, 'American Sniper,' and his co-star Eric Close has revealed that the heartthrob overhauled his diet and fitness routine for the part.

The 'Nashville' star, who plays a Defence Intelligence Agency agent in the film, told E! News: "He put on like 40 pounds. He's really been working hard. He looks great. He's really taken on this character...He really takes this story personally and wants to do an honourable job for Chris' memory and for his family."

The movie, which is currently shooting at the Blue Cloud Movie Ranch in the Santa Clarita, California and also stars Sienna Miller, sees the Navy SEAL recount his military career, during which he killed 150 people, and is due to be released next year.

Bradley, who is dating British model Suki Waterhouse, admitted in February that he had to "go commando" to meet US President Barack Obama at the White House in Washington D.C. because his suit wouldn't fit after he gained 20 pounds for the role.

He previously said: "So I'm prepping for a new movie ... and nothing fits anymore.

"I wore the tuxedo I wore to the Golden Globes. I just sort of threw it in the bag and brought it and went to Washington, D.C., and then I'm getting dressed like 10 minutes before I was supposed to go and literally the pants go up to like here. So I had to go commando; number one, because there was no room at all."