Ansel Elgort Goes Blond & Shirtless in Mexico with Hot GF

Ansel Elgort and his high school sweetheart escaped the bad L.A. weather over the weekend with a trip south of the border ... where they both gave off muy caliente vibes.

The "Baby Driver" star -- who'll soon be the new "West Side Story" star -- was spotted hitting a beach in Mexico Sunday with his longtime girlfriend, Violetta Komyshan ... and they both looked incredible in their swimwear as they packed on the PDA.

Ansel was also sporting a new 'do -- bleaching his normally brown hair blond, and definitely pulling it off too. Violetta, of course, looked hot as hell too au naturel.

The couple has been dating since their high school days at Fiorello H. LaGuardia School in NYC -- and they've been going strong for seven years ever since.