Hitting the Nevada strip, Niall made sure to make his 21st one to remember with a fun night out at Vegas hotspot XS nightclub.
Catching up with his pal and JLS star Marvin Humes, Niall tied in his birthday night out with Marvin's Vegas gig as the Capital FM DJ took to the decks inside the venue before the evening's headliner, David Guetta.
Sounds like a top night out to us!
After getting the club-goers pumped up and ready to go, Marvin wasted no time in joining in with Niall's celebrations and sharing a photo of himself and Niall on Instagram, he said: "Very special night with this guy! Happy 21st Birthday @NiallHoran we tore the place up! Boom!!!"
The pair were reported to be joined by Niall's bandmates, Liam Payne and Zayn Malik as well as 1D's hairdresser Lou Teasdale, but unfortunately 20-year-old Harry Styles couldn't join in the Vegas fun as he isn't quite old enough to drink legally in the gambling city.
One other person who bumped into the birthday boy was singer Joe Jonas - even if it was an awkward run-in in the loos... Oops!
Taking to Twitter, Joe tweeted: "Always nice running into @NiallOfficial when he is on the toilet..."
Always nice running into @NiallOfficial when he is on the toilet..— jøe jønas (@joejonas) September 15, 2014
Still, it makes a good story right?!
On the day of his birthday, the cheeky 1D star thanked everyone for their well-wishes as he still couldn't believe he had hit the milestone.
He tweeted: "Thank you all so much for your birthday wishes , 21 aye? Jesus! Can't believe the love you guys are giving me on my bday! Love you!"
And it seems Niall had another reason to be thankful, as ahead of his birthday, One Direction's new track 'Fireproof' broke records as it became the most downloaded free track in just 24 hours!
The boys' single was downloaded a mega 1,089,278 times. Crazy!
Looks like our 1D boys have definitely still got it!
'Fireproof' features on One Direction's brand new album Four set to be released later this year, just before Christmas.
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