Pop sensation Britney Spears has revealed that she didn't know who Justin Bieber was when they first met because he was only 16-years-old and looked much younger. 

Chatting to BBC Radio 1's Scott Mills this week, the "Make Me" superstar explained that Justin Bieber once came to meet her and she thought he was just "a kid" who had walked into her hotel room:

"He walked into my hotel room and he was like a kid. Literally, he looked like he was 13 years old but he was 16. I was like, 'Who is this kid in my hotel?' And my sister was like, 'This is Justin Bieber and his mother'. And I was like, 'Oh my God, I cannot believe this'. He’s very unassuming. He’s a very, very nice, kind boy."

Spears will take the stage at the forthcoming MTV Video Music Awards ceremony, which is due to take place on Sunday, August 28 at the iconic Madison Square Garden venue in New York City, New York.

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Watch a trailer for Britney Spears' Carpool Karaoke segment below: