They grow up so fast, don't they?
"Happy Birthday @NiallOfficial …Behave yourself. All on red."
Niall behaving himself? Well, that doesn't sound like any fun.
The birthday boy also took to Twitter to celebrate the big 2-0.
"Yesss ! I'm 20 ! Wohoo ! No more teens!" he wrote.
And of course, what would a birthday be without a message from the official band's Twitter? Absolutely nothing.
The account tweeted, "Happy Birthday @NiallOfficial! You can still Tweet your #NiallsBirthdayCake pics—we're loving the results so far!"
Meanwhile, it looks like the other members of the band, Zayn Malik, Liam Payne and Louis Tomlinson have yet to honor their fellow mate.
It seems as though Directioners have been sharing pictures of their own cakes for the heartthrob.
Now that is certainly bound to be a lot of cake!
How are you celebrating Horan's birthday? Tell us below!