Kelly Osbourne Quits 'Fashion Police' ... She Just Had It

Kelly Osbourne quit "Fashion Police" ... TMZ has learned.

Multiple sources connected with the show tell us ... producers and Kelly were at odds even before the Giuliana Rancic showdown, where Kelly threatened to quit unless Giuliana apologized over her comments about Zendaya on the red carpet at the Oscars.

We're told the tension started over the first episode the cast taped without Joan Rivers. Kelly was unhappy with the way the show was being produced. Producers, we're told, were "up to here" with Kelly so the handwriting was on the wall.

Sources tells us Kelly walked Friday.