Mr Penn and Madonna were married in 1985 but divorced four years later
Sean Penn, who is to star in new film Milk, has shared an on-screen kiss with co-star James Franco.
The actor was reportedly so excited about his first gay kiss that he sent a text message to Madonna about it.
Mr Penn and Madonna were married in 1985 but divorced four years later.
Mr Franco said:
"After our kiss, Sean texted Madonna and said, 'I just popped my cherry kissing a guy. I thought of you. I don't know why.'"
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Mr Penn also has to kiss Mart Martinez in the film. Of the kiss, Mr Martinez 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!"
Milk will depict the life of Harvey Milk, Californias first openly gay elected official. Milk was assassinated in 1978.