Bella Hadid hit up a huge Cannes fundraiser in an outfit that definitely raised ... spirits. And other stuff, we're sure.

Bella and her beaded, see-through gown made a ridiculously head-turning entrance -- and exit, no doubt -- at the annual amfAR Gala. It's like the biggest who's who event every year in Cannes ... but the lady knows how to stand out in a crowd.

As for Bella's mystery admirer -- it's not polite to stare.

But we can't blame ya.