Whether you're a fan or not, it's safe to say that Harry Styles is right now, one of the biggest pop stars in the world.

The one-time boybander has become a household name in recent years on both sides of the Atlantic - but it seems not every household has been won over by his charms.

Ashton Kutcher revealed an amusing story in a new interview with Esquire, saying that he had attended hosted by a neighbour of he and wife Mila Kunis. The neighbour is an unnamed famous singer, who got up to do karaoke.

"She was throwing a karaoke party, and she gets up and does this out of this world - bananas - and I’m just like, 'This is so unfair'," he said. "And then this other kid gets up and he does this ABBA song."

The 'other kid' turned out to be Harry Styles, whom Kutcher didn't recognise. He told him: "Man, I gotta tell you something. You’re like a karaoke ringer. You’re really good, like, really good", to which the pop star replied: "Thanks man, thank you. I really appreciate that."

Kutcher then went to the host and said "'God, that guy was really good'. And they’re like, 'It’s Harry Styles'. And I was like, 'Who’s that?'"

The penny finally dropped with Mila Kunis, who told him: "‘It’s the guy from the boyband! He’s like a professional singer!’"

He added: "I just really want to say I’m sorry, Harry Styles. But you’re really good at karaoke, man. Seriously, like really good."

Kutcher is currently starring in 'That '90s Show', while Styles is on his 'Love on Tour' tour in the US.