EXCLUSIVE

The Jonas Brothers Crash Mary Carey's Wedding in Cuba

Hear the one about the Jonas Bros -- formerly of purity ring fame -- running into a porn star at the altar? Well, you're about to, 'cause Mary Carey's Cuban wedding got super random.

The ex-porn star and Dr. Joseph Brownfield had their wedding celebration in Havana and, while partying at a restaurant called La Guarida ... in walked Nick and Kevin Jonas!

Turns out all 3 Jo Bros have been in Cuba too, and just happened to be dining in a separate part of the restaurant. Kev and Nick posed for this shot with the happy couple. Joe abstained.

We're told Nick and Kevin weren't there long, and managed to dodge any wedding singer duties.

You'll recall, Mary and the good doc got hitched in L.A. a couple weeks back, but had the ceremony and reception in Havana. Great timing.

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