Check out Cristiano Ronaldo's longtime lady friend swimming around in the Mediterranean in a tiny, white thong bikini and a pair of flippers.

The insanely fit couple has been sailing around on their fancy, new yacht along the French Riviera ... hanging out with their insanely ripped pals -- living the good life.

Earlier this month, Ronaldo's Juventus squad won their 9th straight Series A -- but didn't win the Champions League, after being knocked out by Manchester City in the quarter-final match.

So, how do you blow off some of that steam? BOAT VACATION!

Of course, 35-year-old Ronaldo and 26-year-old Georgina have been together for years -- and she gave birth to their daughter, Alana, back in 2017.

There have long been rumors about the two being secretly engaged -- or even secretly married -- but the couple has denied that several times over the years.