Sean Penn kissed his male 'Milk' co-star for what felt like "forever".

In the steamy scene, Sean is required to get passionate with his co-star Mark Martinez - who plays the famous cross-dressing disco singer Sylvester - and Mark says he "couldn't believe" how enthusiastic the Oscar-winner was.

Mark said: "I'm performing, and Sean comes onto the dance floor. He grabs me, and he just slaps the biggest kiss on me. It felt like the kiss was forever. I'm like, 'Is he going to stop?' I had to close my eyes, I just couldn't believe it!"

Mark also recalled a scene where he had to sing Sylvester's 1978 hit track 'You Make Me Feel (Mighty Real)'.

He told TV network E!: "All of a sudden, Sean's pointing at me and he's talking to the assistant director. The assistant director comes up to me and says, 'Just to let you know, you are now going to break up Sean and his co-star James Franco's conversation. You're going to grab Sean, and Sean's going to be really excited, and he's going to kiss you.'"

"I wanted to do another take, I'm thinking, we gotta do this thing again. We just didn't get it right. But Gus was like, 'It's perfect, perfect, perfect.' I said, 'No! It's not perfect! Sean was laughing at me during the scene!' "

Sean plays Harvey Milk in the film which tells the story of Milk, California's first openly gay elected official, who was assassinated by San Francisco Supervisor Dan White.

Sean split from second wife Robin Wright Penn last December after 11 years of marriage.