TMZ got ahold of a security tape recorded from an elevator inside the Standard Hotel showing Beyonce's sister Solange Knowles yelling and attacking Jay Z.

Jay Z and Beyonce were attending a Met Gala after party at the Boom Boom Room inside the Standard Hotel in New York.

In the footage, Jay-Z, Beyonce and Solange head into the elevator. Solange appears to be yelling at Jay-Z and corners him in the elevator.

Next, the incident got more intense. Solange lunges at Jay Z, her brother-in-law, throwing punches and kicks. Jay-Z sticks his arm out to defend himself.

A man who appears to be a bodyguard intervenes. He tries to stop Solange from attacking Jay Z. Jay Z casually stands against one of the elevator doors. Beyonce watches the whole thing happen but doesn't get involved.

Finally, Solange makes another lunge at Jay Z and continues to yell at him. The bodyguard holds her back, and then Beyonce finally steps in between her sister and her husband.

The bodyguard allegedly hit the emergency switch in the elevator to prevent anyone from seeing the fight. After the bodyguard gets Solange to settle down, he sends the elevator back up several floors and then finally back down to the lobby.

As the bodyguard and Beyonce head off the elevator, Solange gets one more sneak shot at Jay Z. The bodyguard and Beyonce head back into the elevator and pull her off Jay Z. She still manages another partial punch on him. The door closes and opens a few times, and finally all four leave the elevator.

A source told Us Weekly, "Solange flipped out over something Jay had said, that she took the wrong way. She took it too hard or too far. Not sure what it was, but she greatly overreacted."

After they get off the elevator, all four are photographed. Solange looks visibly upset. Jay Z and Beyonce look calm.

Jay Z's reps as well as Beyonce's reps are staying silent on the incident.