They've won the hearts of young girls everywhere.
And even the stars aren't immune to the charms of One Direction.
But who's their latest celebrity fan?
It's none other than Simon Cowell's ex, Sinitta.
We caught up with her at the Sex And The City 2 DVD launch and, when we asked who she thought would win the X Factor, the word "gush" doesn't quite cover it.
"One Direction, of course. But not just because they're Simon's but because we've never had a group win before and they are genuinely a teen sensation," she told us.
"They're all gorgeous, they all sing. You see the effect Justin Bieber had on the audience and there's five Justins in that group."
And just in case you're wondering who her favourite is, it's Zain Malik.
We also took the chance to ask her about the rumours that Simon and his fiancee, Mezhgan Hussainy, were on the rocks.
"He hasn't discussed it with me, not surprisingly. All we've been talking about is the X Factor final, Britain's Got Talent and American X Factor. He's so focused, it's all about work for him at the moment."
But if, and when, the couple do make it down the aisle, what can Mezhgan expect?
"I love the buzz and the energy of being with Simon. It's relentless but you learn so much, it's never boring, she said.
"He does know how to relax though which is a good thing. We have lovely holidays but even on holiday you're working because he's so creative that he's still throwing ideas around and getting reactions and feedback all the time."
It sounds exhausting. Good luck, Mezhgan.
By Suzannah Ramsdale
