One Direction star Niall Horan has admitted he is still in shock over the success of the boyband.

The British quintet have just touched back down in the UK after a debut headline tour of North America.

Speaking to MTV News, Horan said that the band never expected to enjoy so much success around the world. He said:

"To be honest, if you had said to us a year ago, and this sounds so clichéd, [but] if you had said to us a year ago that we were gonna be touring America, we would absolutely have fell on the ground laughing at ya."

Horan added that their record label's decision to send the band to America was taken without really knowing how they would be received. He added:

"Obviously when the record label and stuff wanted to send us to America just to see how it would go, no one, not even them, had an idea of how it was going to go. And self-admittedly no one could tell how it was going to go. So to think that we're going on a world tour next year and about 85 percent of it is sold-out already is just mind-blowing."