Solange Knowles kicks, punches, claws Jay-Z in elevator: A surveillance video has surfaced showing Beyonce’s younger sister attacking her brother-in-law, although it’s unclear what caused the altercation.

Jay Z and sister-in-law Solange Knowles had an altercation at a Met Gala after-party May 5 that was caught on tape, obtained by TMZ.com.

It all went down in an elevator where the 27-year-old sister of Beyonce can be seen clawing and kicking at her brother-in-law as the “Halo” singer looks on.

It’s unclear what caused the argument as there is no sound on the black and white surveillance video, shot after the group attended a soiree at the Boom Boom Room at New York’s Standard Hotel. “Solange flipped out over something Jay had said, that she took the wrong way,” a source told Us Weekly. “She took it too hard or too far. Not sure what it was, but she greatly overreacted.”

A source tells the Daily News Solange’s demeanor appeared dramatically different just hours before when she attended the Met Gala. She was seen smiling at the fete and described as being in high spirits.

However at the after-party, as the group walked into the elevator where Beyonce already stood, Solange appeared to immediately begin screaming and pointing in the “Holy Grail” rapper’s face.

While it seems he had some words of his own, when Solange began attacking him, Jay Z looked like he was trying to hold her arms down as another unknown man, presumably a bodyguard, held her back.

It appears the bodyguard attempted to keep the altercation private by pressing the emergency stop button on the 12th floor repeatedly.

Beyonce initially remained calm and leaned against the elevator wall. She finally appeared to say something to Solange after she broke free and approached Jay Z again, kicking and punching.

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Beyonce, Jay-Z and Solange Knowles were seen leaving the Met Gala After Party at the Boom Boom Room in the Meatpacking District.

At one point Solange smacked Jay Z with her purse as its contents flew out spilling all over the floor of the elevator. The “99 Problems” rapper eventually leaned down and picked up the purse handing it to his wife.

But that didn’t stop Solange as she continued attacking him.

She then walked ahead of the couple as they exited the elevator and did not look happy as the bodyguard handed over her purse. Jay Z strolled behind his wife, who surprisingly seemed to be smiling.

A different video shows that as the group approached the same car to leave, Solange got in first as Jay Z stepped aside to allow is wife to get in. He then proceeded to another vehicle and left separately.

Shortly after the footage was posted online, The Standard Hotel said they were “shocked and disappointed that there was a clear breach of our security system.”

In a statement issued to the Associated Press, the venue said it plans to investigate the leak of the video and “will discipline and prosecute the individuals involved to our fullest capacity.”

Reps for Beyonce, Jay Z and Solange have yet to respond to the Daily News’ requests for comment.

Watch the Full Fight Below courtesy of TMZ