Drake did the impossible ... by escorting his little cousin and her date into prom, he actually made it cool to have a chaperone. Just this once.

Drizzy did his cuz, Jalaah Moore, a major solid by showing up this weekend in Memphis. And as you'd expect ... he spoiled the couple and made 'em total ballers. Sources close to the family tell TMZ  Drake flew in Saturday ... ordered them a white Rolls Royce to drive them to prom, and also paid for their custom matching outfits.

Drake also crashed the dance at Fairley High School -- major social points for Jalaah -- but we're told he didn't perform ... just hung out. We imagine the other chaperones were as starstruck as the kids.

Afterward, he threw Jalaah a party at Hard Rock for about 400 of her suddenly super-close friends. 

BTW, Drake's dad is Jalaah's grandma's bro. So, yeah ... best 2nd cousins ever!

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