Tyga & Blac Chyna -- Broken Up!!!

Call off the wedding ... Tyga and baby mama Blac Chyna have split.

Sources close to the former pair tell TMZ ... Tyga's the one who called it quits. It's unclear why he threw in the towel.

We're told Blac Chyna isn't acknowledging the breakup -- she's in denial -- and some of her stuff is still at the house.

We're told Tyga hosted two pool parties at their home in the last few weeks (including one for Kylie Jenner's birthday) but she wasn't invited to either.

The couple has been together since 2011 and got engaged in December of 2012. They have a son -- King Cairo -- who turns two in October.