James Corden has revealed Mark Ruffalo helped him unwind on the set of Begin Again - with a relaxing gin and tonic hidden in a coffee cup.

The British actor appears with Mark in the improvised romantic comedy about a washed-up record boss, played by Mark, who takes a shine to an aspiring singer-songwriter, played by Keira Knightley.

James revealed: "Mark's adorable, he's just great. He's fantastic. I was doing a play in New York at the same time as the film, so there were quite a few days where I'd shoot like 12 'til six in the afternoon and then I'd get in a car and go across the city and do a play and then I'd be back after the play, because there's quite a lot of montage stuff where we'd need to shoot at night.

"There was this one day where we were shooting on the subway. No one had any lines, it was just this montage of us playing music and Mark had this flask of coffee and he said, 'Oh man, you look exhausted. You must need a drink.'

"And I went , 'Yeah, that'd be nice!' And he gave me his coffee flask and I tried it and it was like gin and tonic! And I just went, 'Oh, that's great!'

"And he went to his assistant or someone, 'Can we get James one these coffees?'."

In the film James, who plays Keira's character's best friend, lives in a tiny studio in New York, and James revealed he could relate to that.

He said: "Before I met my wife I shared a flat with an actor called Dominic Cooper, who's one of my best friends, and we rented what was called a furnished apartment, and there was very little furniture in it.

"Our intention was always to get more furniture, but we never did.

"It was quite a big room with a kitchen in it and we had a tiny, tiny, two-seater sofa, one of those awful leather ones with silver bars like you get in a waiting room of an office. We had that and a coffee table and a TV. And I didn't have a bed for a while, I had a mattress on the floor.

"But they were some of the best times I've ever had. It was great."