Robert Pattinson has suggested that it's the 'total commitment' from the characters Bella Swan and Edward Cullen that makes young fans so dedicated to the series.
The British actor reprises the central role of vampire Edward in New Moon this week, a film that has already become the biggest pre-release movie of all time.
In an interview with BBC's Newsbeat he said: I'm not entirely sure what the young girls see in it because I didn't know young girls were lusting after a relationship about total commitment. I didn't know that was such a sexy thing.
"It's about a guy who will totally and utterly commit to you and yet it will never get too safe - which is, I guess, the bad point of a committed relationship. "
He added: "I think people hold up the Edward/Bella relationship as a kind of ideal or something and people are desperate to reach for it.
"I really don't know why, it's obviously just touched people in a very profound way."
And Twilight Saga fever looks set to continue with Eclipse, the third movie in the series, hitting screens next summer.
New Moon is out now.
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