Rob Gronkowski Flashes His Penis to Supermodel?

9:23 AM PT -- We asked GQ if Gronk was really fully naked for the shoot.

The answer -- "Yes, he was naked."

Boom.

So, here's a pic from Gronk's highly anticipated GQ article ... in which the photo shoot motivation was apparently, "Surprise! Here's my dong!"

The flashee in the shot is supermodel Hailey Clauson -- who teamed up with the Pats tight end for the cover of the upcoming June issue of the magazine.

The guy who wrote the article about Gronk spent some time embedded with the NFL star and described his life the following way:

"Gronkowski seems to exist in a permanent shower of champagne spray and nightclub-foam-party foam ... all without ever seeming like a creepy douchebag.”

#GronkJustBeingGronk