Why Beyonce's sister Solange Knowles kicked and punched Jay Z?

Solange Knowles reportedly attacked Jay Z after she "overreacted" to something he said.

The 27-year-old singer "flipped out" at the rapper, 44, in an elevator at the Met Gala after-party in New York last week because she was offended by a comment he made.

A source told Us Magazine: "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."

(L-R) Actress Jessica Biel, singer Beyonce, rapper Jay-Z and singer Solange Knowles attend the 55th Annual GRAMMY Awards at STAPLES Center on February 10, 2013 in Los Angeles, California. (GETTY)

Solange was caught on surveillance kicking and clawing her brother-in-law as they left the bash held in the Boom Boom Room at The Standard Hotel in New York City, last Monday (05.05.14).

Jay Z didn't appear to retaliate as the brunette beauty screamed in his face, but he did attempt to hold her hands and foot down as their bodyguard struggled to hold her back.

Beyoncé appeared to stay calm and collected throughout the scuffle and watched on helplessly as her sister violently attacked her husband.

Designer Phillip Lim Solange Knowles attends the 'Charles James: Beyond Fashion' Costume Institute Gala at the Metropolitan Museum of Art on May 5, 2014 in New York City. (Getty)

However, at one point, the 'XO' hitmaker - who has two-year-old daughter Blue Ivy with Jay - intervened and said something to Solange after she began punching him again.

Solange then stormed out of the elevator with a disgruntled expression plastered across her face as Beyoncé, 32, and Jay Z followed shortly behind.

The siblings were then seen getting into a car together, while the 'Holy Grail' hitmaker opted to travel alone.

Jay Z holds his face as Solange marches ahead angrily minutes after attacking him in the elevator. (BANG)

Solange Knowles viciously attack

Beyoncé's sister viciously attacked Jay Z at the Met Gala after-party in New York City last Monday (05.05.14).

In the footage, obtained by TMZ.com, Solange screamed in his face and kicked and punched him. The bodyguard in the lift tried to hold her back.

The bodyguard can even be seen pushing the emergency stop button repeatedly as the elevator reached the 12th floor in a bid to keep the violent altercation private.

Beyoncé - who has two-year-old daughter Blue Ivy with Jay - finally intervened and said something to Solange after she broke free and began punching him again.

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