Simon Cowell has warned One Direction to slow down.
The 55-year-old media mogul - who helped to put the group together on 'The X Factor' - has revealed that he fears for the five-piece boy band.
He said: "They can't carry on doing the amount of stuff they've been doing for long because they'll burn out - it's a high-class problem.
"But they don't complain about working hard."
The 'Steal My Girl' hitmakers - who will embark on their third world tour next year - are "generous" to their fellow artists, according to the talent show judge.
He explained: "They still come down to 'The X Factor', into song meetings and they will text me with ideas for the contestants.
"They're generous to other artists. You don't see that very often. Most artists couldn't give a damn about anyone but themselves!"
Simon also revealed that the boy band - which consists of Harry Styles, Liam Payne, Niall Horan, Zayn Malik and Louis Tomlinson - put their success down to their unique relationship with their fans.
He told The Sun newspaper's TV magazine: "They're going to be around as long as they want to be, because they're talented and good writers - and they understand their fans."
Meanwhile, Simon recently admitted that he still regrets that the act he mentored on the ITV talent show didn't take the main prize.
He said: "I still can't watch the moment when One Direction came third.
"I was so arrogant about the fact we were going to win that I was waiting for someone else's name to be called out.
"Even though they've done well I would still like history to have said they had won 'The X Factor'."
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