Rihanna Caught Making Out Hard With Sexy Mystery Man In Swimming Pool

(TMZ) -- Rihanna's getting along swimmingly with a guy we're hearing might be her new boyfriend ... and it couldn't be clearer they can't keep their hands off each other.

RiRi and the guy -- we don't know who -- were making out in a pool ... and all over each other for sure.

The pics were taken in Spain on Monday, where it appears she's vacationing with him. They're staying in a posh villa.

She was a no-show at the BET Awards ... she clearly had a better offer. See the steamy photo here!

Photo: Getty Images