WATCH: Rob Gronkowski stars as 'grown up' in hilarious Foot Locker spot

When healthy, New England Patriots' Rob Gronkowski is the NFL's top tight end. He's also one of the biggest, which makes him so dominant.

Standing at 6-foot-6, 265 pounds, no one would be inclined to say Gronk looks like a little kid. But even still, he plays the game with such passion and enjoyment that you could argue he looks like a kid playing football. From the "Gronk Spikes" to his dance moves on the sidelines, he isn't exactly the most grown up of grown ups, and that's what makes him a fan favorite.

If you didn't think Gronk was a little kid in a grown man's body before, maybe you will after watching this hilarious ad for Foot Locker.

The secret's officially out. Now everyone knows what Gronkowski does when he's not running routes, scoring touchdowns, and spiking footballs. Oh, and singing about iced coffee with his buddy David Ortiz.