A rep for the South African actress/model tells TMZ Dean passed away Monday from an unexpected sudden illness. We don't yet know what illness Dean was fighting, but a source tells us she died in a hospital in NYC.

Dean recently landed her biggest role in "Triangle of Sadness." It hasn't hit theaters just yet, but it did impress at this year's Cannes Film Festival ... where it took top honors with the Palme d'Or award. It's about a wrecked cruise ship and its passengers getting washed ashore, Charlbi is the lead, starring opposite Woody Harrelson ... the cast made a big splash in France in May, showing up at events and hitting red carpets together.

When their film won, Charlbi wrote ... "Congratulations our family we did it!!! @ruben_ostlund you're the GOAT I'm forever thankful for you for trusting me to be apart of your genius and my dear @sinaostlund Can't believe I had the best year making this during one of the hardest times in my life. Here's some pics of the year in Sweden and Greece during the pandemic. Forever and always our @triangleofsadness family."

She is also known for her work on the CW show "Black Lightning," where she played Syonide ... an assassin/hitman-type of anti-hero who's got bulletproof skin and top-notch combat skills. Other films she's worked on include "Blood in the Water," "Don't Sleep," "An Interview with God," and "Porthole."

She's also walked her fair share of runways and graced a number of magazine covers too ... CD has modeled all over the world.

Charlbi was engaged to male model Luke Volker. She was 32.