The polite Brit admits he was more than a little embarrassed when he couldn't control his penis while filming TV period drama The Tudors with an unnamed co-star.

Cavill, who played Charles Brandon on the show, tells the new issue of Men's Journal, "A girl had to be on top of me, she had spectacular breasts, and I hadn't rearranged my stuff into a harmless position. She's basically rubbing herself all over me and... it got a bit hard.

"It's not great when you're in a professional acting environment and somebody gets a boner (erection), is it? No, not acceptable."

The actor "profusely" apologised to the actress in question and admits he has never been a fan of shooting sex scenes.

The Man of Steel star adds, "It's actually acutely uncomfortable being naked in a roomful of people. The very last thing it is is sexy. The actual physicality is very uncomfortable. All you're doing is smacking your nuts against someone, and nothing is going in."