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The Belieber (as Justin's fans are known), 14-year-old Amilia Radevska, saw a hole in the beefed-up security team, and decided to make a break for it. As Brian stepped in and restrained the wayward teen, she apparently kicked and screamed "stop it Brian".
The attempted mobbing went down as AGT host Grant Denyer interviewed Justin after his performance, during which the pop star sang a six-minute medley of his biggest hits.
About 800 tickets to the show were given away via radio competitions, with around 1,000 fans actually showing up to wait outside the Docklands studios in Melbourne, trying to catch a glimpse of the Canadian-born singer.
During Justin's 2010 visit to Sydney, his planned Sunrise concert at Circular Quay was shut down by police due to unsafe conditions, leaving 5,000 Beliebers to storm the Sunrise studios in Martin Place. The singer was snuck into the Sunrise studios to perform one song, driving the fans crazy.WATCH: Justin Bieber wanted for questioning over Calabasas scuffle