Donald Trump Jr. laid one on his gf, Kimberly Guilfoyle, while vacationing in the South of France ... the first time they've put on any PDA in public.
Jr. and gf K.G. relaxed at Nikki Beach in St. Tropez Friday ... where it looks like he mostly went unnoticed under his straw hat and sunglasses.
Can't blame the dude for wanting to keep a low profile overseas with all the protests in England over his dad's visit.
The couple snuggled up on a couch by the pool and Don also took a hit of a hookah, which we're guessing was filled with tobacco ... then again, who knows?
The FOX News host and Prez's son have been dating for a while now. His wife, Vanessa, filed for divorce in March but says she has no issues over her estranged hubby's new romance.