Harry Styles overwhelmed by success

Harry Styles has thanked his fans in a heartfelt tweet.

The One Direction heartthrob is celebrating three years with his bandmates Zayn Malik, Liam Payne, Louis Tomlinson and Niall Horan.

Having just released the video for their hotly-anticipated single Best Song Ever has clearly caused the 19-year-old to reflect on his success.

"3 years.. I honestly can't believe it. Thank you so much for everything, we're so lucky to have you. You keep making it more and more fun (sic)," he posted on Twitter.

The band was formed on the UK edition of The X Factor in 2010 and despite not winning the show, One Direction have gone on to become one of the competition's most successful acts.

In their new music promo, the boys take on a selection of funny alter egos.

Zayn dresses up as a woman for the clip, while Harry plays a nerd, Liam a camp choreographer and Niall and Louis take on the roles of music industry bigwigs.

As well as promoting their new track, the boys are busy with their Take Me Home Tour.

Currently on the North America leg, they seem to be having a great time.

"Thank you Dallas for an amazing night. You were so loud. Thanks for having us Texas (sic)," Harry posted, reminding fans: "I was asleep... But the video for 'Best Song Ever' is on Vevo now! Go watch it six times and let us know what you think. Hope you like it .x (sic)"

Meanwhile, it's been reported Harry is keen to shape up for the summer.

According to the band's fitness trainer, Mark Jarvis, the star has banned sweets from the tour bus.

"The lads want to get defined beach bodies," he told British newspaper Daily Star.

"Lots of protein is the best way for them to get in shape and build up muscle.

"Harry has heard about this new healthy ice cream and is really fascinated by it."