Well, according to her bandmate Jesy Nelson, Leigh-Anne got so excited that it was like all of her Christmas' had come at once! Or more precisely, she was "like a little child who's just seen Santa"!
Jesy very kindly told the story as the girl band spoke to Nick Grimshaw on BBC Radio 1.
"Leigh-Anne is the biggest Justin Bieber fan ever," said Jesy. "Like, when we were in the X Factor house, I'm not joking, she put up posters on the wall in the X Factor house. Her bed was smothered in Justin Bieber.
"So she's never met him before. Anyway, she was getting her make-up done, and he walked in the room but she had her back facing him. And he walked in and I was like, 'Leigh-Anne? Um, Justin Bieber is standing right behind you'.
"Her face... You know like a little child who's just seen Santa?"
Perhaps somewhat embarrassed, Leigh-Anne told Jesy: "Stop it!
Little Mix are currently promoting their third studio album Get Weird, which is out now.
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