Katie Couric and DJ Pauly D: When worlds collide!

It's "Jersey Shore" meets the Hamptons on the set of "GMA." Katie Couric -- who will be guest-hosting the morning show starting Monday (April 2) tweeted out the pic with the caption, ""So....this happened. Never know who you'll run into at @GMA!"

The chain-biting thing is almost as troubling as Pauly's Season 1 stalker.