They have remained friends even after their boy band One Direction went on hiatus.
But the sight of Harry Styles can still get a shout of panic out of Niall Horan.
Niall, 24, swung by The Ellen DeGeneres Show and let out a yell when a screaming Harry lookalike suddenly popped out of a hollow table near him.
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Fancy dress: Niall Horan swung by The Ellen DeGeneres Show and let out a yell when a Harry Styles lookalike suddenly popped out of a hollow table near him
The crowd went wild and the Harry impostor ran offstage.
Niall quickly regained his composure as Ellen smirked at him.
'I honestly - cardiac arrest nearly happened there. Why is it not just straightforward on this show?' said Niall with a laugh.
Surprise: 'Harry' was wearing a pink and coral print jacket over a retro-chic ruffled shirt, screaming as he sprang from his hiding place
He leaned into the empty hiding place and plucked out a couple of pink knee pads that had been left down there for the Harry lookalike's benefit.
Niall mimed tossing them out into the crowd, jokingly announcing: 'And there's one for everyone in the audience!'
Ellen then replayed - with Niall still sitting there - the clip from a