Solange's flare-up 'happened before'

Solange has always been known as one of the cooler chicks in the music industry, but does she have a tempestuous side to her?

According to US Weekly, Jay-Z, 44, and Beyoncé, 32, weren't too surprised by the younger Knowles sister's latest violent outburst.

The incident was caught on surveillance cameras in an elevator at the Standard Hotel, New York City, following last Monday's Met Gala after-party.

In the footage, a furious Solange physically attacks Jay-Z, shoving and kicking at him repeatedly.

In fact, a source told the magazine: "This is not the first time this has happened. That's why Bey and Jay were so calm. They are used to this from Solange."

Apparently the Losing You singer was also pissed off earlier that evening at designer Rachel Roy, and "inexplicably yelled" at her. The reason for the outburst is unknown.

A video of the fight was leaked this week by celebrity website TMZ, sparking a social media storm.

In the footage Solange, 27, is seen shoving Jay-Z in the hotel elevator.

A bodyguard tries to restrain her as she kicks at the rapper. Beyoncé looks on as one of the kicks hits Jay-Z's thigh.

Photographs taken of the celebrities moments later show a pensive-looking Jay-Z, holding his left cheek, while a smiling Beyoncé appears completely unfazed.

The two sisters are then led into one limousine while Jay-Z leaves the hotel in another vehicle.

The UK's Daily Mail found body language expert Judi James, who analysed the video and came up with possible reasons for Beyoncé's cool reaction to the fight.

"The singer's lack of physical reaction implies that she has witnessed this type of behaviour from Solange before," James said.

"Half-way through the clip, the singer does stand in between the warring pair, which is probably more to stop her sister getting hurt, rather than to protect Jay-Z."

Some theories on social media include a possibility that Jay-Z cheated on Beyoncé with someone also at the Met Ball, and Solange was letting him know what she thought, while others think she was having an episode.

Page Six recalled her cancellation of European tour dates due to "mental/physical health" reasons.