Not sure what triggered this family feud, but after the Met Gala last weekend Solange Knowles was not too happy with brother-in-law Jay-Z.

Solange, Beyonce and Jay were all heading into an elevator after the event when the fight broke out. Of course TMZ got a hold of the video and as you can see, Solange is angry!

She starts yelling in Jay's face, then gets physical with fists and feet flying. A bodyguard is there to break things up, but she gets a few hits and kicks in.

Looks like Beyonce wants nothing to do with the altercation, just standing back and observing.

Again, no idea why she was so angry, but I'm sure we'll start hearing rumors on that soon enough.

**UPDATE: Onlookers the night of the event say Beyonce left the Gala with her sister, not with her husband. Solange got into a waiting car, Jay-Z paused before choosing to take another vehicle home and Beyonce climbed in after her little sis. Now I really want to know what the fight was all about!