Channing Tatum and Jamie Bell competed to see who could stay in freezing water longest on the set of 'The Eagle'.
Although Jamie revealed the pair hit it off while working together on the medieval adventure film - about a young Roman officer in Britain trying to restore his family's honour with the help of his slave - he admitted they were constantly pushing each other to see who could be better.
Speaking at the film's UK premiere at the Empire cinema on London's Leicester Square, Jamie told BANG Showbiz: "I think the bromance thing generally happens when it's so physical and also when you're in a remote place you can't help but come together. That's kind of what keeps it together.
"It was great, we were very competitive with each other, to see who could ride their horse faster, who had the best fight scene and who could stay in the freezing water for longer."
Asked who usually won their mini competitions, Jamie admitted each had their own strengths with him beating Channing at horse-riding but the American actor coming out on top in the fight scenes.
He said "It depended on what we were doing, I had the fastest horse which I like reminding him about. Channing is great physically, he grounds all of his characters in his physical fitness so his fighting was unbelievable."
Other stars to attend the premiere included former 'X Files' star Gillian Anderson and TV presenter and actor Stephen Fry.