Solange Knowles reportedly had an argument with a fashion designer before her alleged altercation with Jay Z.

Yesterday TMZ released a video which seemingly showed Solange lashing out at her sister Beyoncé's husband in an elevator after they had attended a Met Ball after-party. A person purported to be Solange was seen punching and kicking the hip-hop superstar, with Beyoncé apparently also in the lift - although she didn't get involved.

It's now been claimed that earlier at the bash, which was held at the Boom Boom Room in the Standard Hotel, Solange had a disagreement with Rachel Roy.

According to Us Weekly, Solange began shouting at a group of people, including Rachel. Beyoncé then "got in the middle of it", apparently to try to ease the tension.

It's unknown what Solange and the designer disagreed on, especially as they were thought to be friends. In 2012 Solange accompanied Rachel to the Met Gala, which is seen as the Oscars of the fashion industry.

There has also been no comment on what caused the show of emotion between Solange and Jay Z, especially as the pair and Beyoncé seemed to be having fun earlier in the evening. The siblings were seen busting some moves alongside supermodel Naomi Campbell on the dancefloor, although the rapper "hung back at one of the fireplace areas".

According to an insider the three stars left "abruptly", but didn't appear to have fallen out.

In the video footage, Solange is apparently seen backing her brother-in-law up towards the wall of the elevator while seemingly yelling at him ferociously. She is then seen throwing punches and hitting out with her legs, with Beyoncé initially standing to one side and then appearing to attempt to intervene. At the moment it hasn't been confirmed whether the people in the footage are the famous family.

"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," an insider claimed.

A bodyguard clung on to Solange and also pushed the emergency stop button in an apparent effort to contain the situation.

When the trio left the elevator, Solange walked out first with an unimpressed look on her face, while Beyoncé followed with a smile painted on. Bringing up the rear was Jay Z, who looked stunned.

"Beyoncé tried to stay out of it," another source said. "She does not approve of violence. They are trying to put the situation past them now."

Beyoncé's people have said they won't comment on the footage, while representatives of The Standard Hotel have spoken of their shock and disappointment over it.

Jay Z and his wife attended a basketball game in New York City on Monday night, around the time the video was released. He refused to comment on it, but looked relaxed and happy alongside his spouse.