One Direction star Niall Horan has spoken out in praise of this year's X Factor contestants.

The singer turned up at the show's set in London on Saturday (October 11) to check out the latest batch of contestants.

It seems the Irishman left impressed by the standard of the acts, with Horan writing on Twitter on Sunday (October 12):

"Great to be back down @TheXFactor last night, the standard this year is super high! Congrats to everyone last night, you killed it!"

Photos of Horan - who appeared on the X Factor in 2010 - with various contestants has since appeared online, including an image with Stereo Kicks' Jake (see above).

One Direction meanwhile released their new single 'Steal My Girl' today (October 13) in the UK.

It is the first official single from the band's upcoming album 'FOUR', which is scheduled to land on November 17.

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Watch clips from this weekend's X Factor below: