As the boys tour the U.S., the 19-year-old is apparently being mobbed by fans, while Harry Styles, who is arguably the biggest star back here, is left in the wings.
And Zayn Malik is apparently not far behind.
'All the boys are popular, but the girls in the U.S. seem to be absolutely obsessed with Niall,' a source told Closer magazine.
'They love the fact he's Irish and looks like the perfect all-American boy. He gets swamped with girls wherever he goes.
'Zayn is a close second - he's very cheeky and confident, which is going down well. It's definitely been a bit of a knock to Harry's ego, as he's used to being the heartthrob back home. It's only natural that the boys are now competing for attention. It's causing a bit of tension.'
A friend added that the band were trying not to 'get on each others' nerves ahead of their three-month U.S. tour which starts in May.
They will play at 20 venues.
'The boys are feeling a bit cooped-up, as they're spending 24/7 together, and are starting to get a little homesick,' the friend said.
'They don't want silly rows to affect them, so are trying to keep fighting to a minimum.'
The boys were pictured arriving at Toronto Pearson airport over the weekend, and yesterday at Montreal airport.
'a source, a friend'....lmaooo
Anyway, more Harry for me! :D