We're not sure if he's a friend, relative or private surf instructor, but we DO know that the guy who accompanied Gisele Bundchen to the beach in Costa Rica yesterday is smokin' hot!

The Brazilian beauty put her 13-month-old daughter on a board with the help of the mystery man, and the tiny tot looks like she had a blast splashing in the waves. Gis has been in Costa Rica with her family and for a few bikini shoots, but it seems like this is more of a leisurely getaway than a biz trip. The other day she toted Viv around while riding on an ATV, and she's been spending quite a bit of time with her dogs too. But where are hubby Tom Brady and their boys?!

Seriously though ... her body looks like this after two kids?! Unreal...