Derek Bieber is a made up person by Justin Bieber, saying he's a look-a-like.
Story
Justin Bieber was being followed by a cameraman from TMZ when he was in Hollywood. At first, he answered all of the cameraman’s questions. But then, he got bored and jokingly said that his name is Derek Bieber, and he is just a Justin Bieber look alike. The young pop star said: “I’m just a look-alike. I don’t know why you guys are following me around with cameras.”
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Justin Bieber -- I've Never Heard Anyone Complain I'm a Brat -- Derek Bieber