Niall Horan has pneumonia

Niall Horan's told fans on Twitter that he has pneumonia.

The One Direction star tweeted on Monday to say he had a chest infection, then later went on to say it was something worse than that.

Get a chest infection Christmas week .... cool cool cool ........ not ideal

— Niall Horan (@NiallOfficial) December 19, 2016

Now he says he wishes he'd listened to his mum when she told him "don't go out with wet hair or you'll get pneumonia".

Should have listened to my mother years ago when she said " don't go out with wet hair or you'll get pneumonia"

— Niall Horan (@NiallOfficial) December 21, 2016

Mammy knows best, Niall.

The Irish star, who recently launched his debut solo single This Town, will be hoping he gets better before New Year’s Eve, when he’s set to perform in Los Angeles.