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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.