The 'Best Song Ever' singer was among the crowds at London's O2 Arena on Monday evening (9 June) to watch singer-songwriter John performing.
Unlike most of the crowd, however, he got backstage to meet the man himself!
Niall uploaded a picture of himself and John to Instagram, adding the caption: "Great tp see John tonight! He was unbelievable as per usual!"
It's not the first time Niall's met John – an idol of his.
The star – who plays guitar himself – was introduced to John following a gig last year, and even walked home with John's guitar!
"Met the best guitarist of our generation last night," said Niall at the time. "Unbelievable musician, great guy! After Gravity he walked over, handed me [his guitar]. Legend. One of those moments."
Apart from singing, songwriting and guitar playing, Niall and John do have one other link: Katy Perry. She's John's ex-girlfriend and a friend of Niall's.
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