Robert Pattinson "doesn't understand girls".

The 24-year-old actor's 'Twilight' co-star Ashley Greene claims the heartthrob - who first found fame playing Cedric Diggory in 'Harry Potter and the Goblet of Fire' - is constantly bemused by the attention he receives from women.

Despite his sex symbol status, Ashley has never had a crush on Robert - who is dating his other 'Twilight' co-star Kristen Stewart - because they lacked "chemistry", though she thought about dating the franchise's Kellan Lutz.

The 23-year-old screen beauty added: "When I met Rob, I didn't think twice about him. He's really attractive, but that chemistry wasn't there.

"Have I hooked up with Kellan? I've definitely thought about it. But he's one of my best friends, but if we were going to be romantic, we would have done it years ago. I like having him to talk to about other guys to get that male perspective. I really cherish our relationship, so I wouldn't want to mess that up by dating."

Meanwhile, Robert claims he has cut off his long locks because he had head lice.

He joked: "I got a terrible infestation of nits and I had to shave it all off."