Richard Drew / Invision/AP 1 / 5
Richard Drew / Invision/AP 1 / 5

Daniel Radcliffe was sure that Justin Bieber was a girl.

The "Harry Potter" star admits he struggles to keep up with current hot pop stars, but had heard Bieber's hit "Baby" on the radio -- and believed the 16-year-old's high-pitched vocals belonged to a female.

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He tells, "I only heard Justin Bieber for the first time two weeks ago. I genuinely thought it was a woman singing. I'd never heard it before.

"I'm so out of the loop when it comes to pop culture that I kind of don't even try anymore."

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But there is one superstar the Brit can't help but notice: he's a huge Lady GaGa fan.

He adds, "I know who Lady GaGa is. I think she's kind of amazing. She's really got a voice. My God. Not my kind of music, particularly, but she can really sing."

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