EXCLUSIVE

Clint Eastwood's daughter got super bad in Vegas last week ... the reality star got hitched to Jonah Hill's brother ... TMZ has learned.

We got hold of the marriage license -- filed with the Clark County Recorder's Office -- showing Francesca Eastwood and Jordan Feldstein sealed the deal Sunday.

Our sources say vows were said at the Simple Wedding Chapel ... a quickie marriage spot that offers Elvis witnesses.

But the marriage is shrouded in mystery! Francesca was out in Hollywood Thursday night and she wasn't wearing a wedding ring. So was it a drunken escapade or the real deal? Only Elvis knows.