Hip-hop superstar Wale just revealed a super awesome branch of his family tree ... telling TMZ Sports Washington Nationals slugger Bryce Harper ... is his actual cousin.

Wale was out in L.A. when we decided to do a little D.C. sports rundown with the DMV representer, asking about the Wizards and then about Harper ... who's currently tearing up the Major Leagues.

That's when Wale dropped the bombshell that's sure to make Donald Sterling's skin crawl ... telling our camera guy that he loves Harper ... mainly because Bryce is actually his cousin!!!

Ok ... so maybe he was joking ... but maybe he's not ... why can't they be related?

Watch the clip ... and open your freakin' mind.