Hollywood hunk Zac Efron is baffled by his pin-up status - because he was such a nerd at school.

The High School Musical heart-throb was swamped by screaming girl fans at the premiere of the film franchise's third installment in London this week.

And he admits he didn't think he would turn out to be such a ladies' man - because he was a geek in the classroom.

He says, "Things can get crazy in terms of the publicity. I grew up as a regular person and want to keep it that way. I never used to get much attention from the chicks. I got good grades at school - in fact, you'd have called me a nerd."