The 27-year-old was caught on surveillance camera lashing out wildly at her brother-in-law, 44, with both her arms and her legs, while her sister stood beside them looking curiously impassive.
The famous family were in an elevator descending from a soiree that followed the annual fashion fest at the Metropolitan Museum of Art.
The seemingly unprovoked attack plays out in footage obtained by TMZ.
Solange can clearly be seen kicking and swinging violently at Jay Z, the father of her two-year-old niece, Blue Ivy, after the trio step into the elevator.
|Solange Knowles attacks Jay Z in lift after Met Gala|
In the footage, a man who looks to be a bodyguard tries to hold Solange back but she manages to rain blows on the rapper several times, and even hits him with her purse.
During the frenzied altercation, Jay Z grabs her stiletto clad foot to block a kick but never attempts to retaliate.
Beyonce seems sanguine throughout, and appears to be trying to calm her sister down.. . at one point she pragmatically removes the long train of her Givenchy Haute Couture dress from the fray.
The bodyguard can also be seen pushing the emergency stop button in the elevator at the 12th floor, no doubt stop the fight spilling out in front of photographers.
Jay Z’s shocked appearance and hand to face as Solange marches angrily ahead after leaving the elevator were captured on film, however.
Beyonce tried to muster a showbiz smile as the threesome left but then tellingly departed with her sister in a car while her husband left separately.
It’s not yet known what provoked the fight, however, the famous couple looked as happy as ever as they attended a Brooklyn Nets game on Saturday while Solange played a gig in New York.
While there still has been no word from either Beyonce or Jay Z’s representatives, a spokesperson from The Standard Hotel in New York City has made a statement. Following calls regarding the leaked CCTV footage, reps for The Standard Hotel told MailOnline, they were ‘shocked and disappointed’ in what had been a ‘clear breach of our security system’.
They said in a statement: ‘We are investigating with the utmost urgency the circumstances surrounding the situation and, as is our customary practice, will discipline and prosecute the individuals involved to our fullest capacity.’
|Tense- In a surprising move, Beyonce left the venue with her sister after the drama|
On Sunday, after the Webster Hall gig with M.I.A, Solange Tweeted: ‘This might have been top 10 days ever in life.’
According to Radar, Jay Z and Beyonce seemed distant as they arrived at the Standard Hotel’s Boom Boom Room, a far cry from the adorable show they made of a schmaltzy proposal on the red carpet earlier at the Vogue party.
Beyonce had dropped a ring and her husband was quick to hit the deck and retrieve it, before recreating the moment he asked her to become his wife.
That was a typically envy inducing show of togetherness, like Mr and Mrs Carter’s performance at this year’s Grammy Awards.
At the Standard, away from prying eyes, the couple sat at a table together deep in conversation before Beyonce peeled away to party with her sister and stars like Lupita Nyong’o.
According to Us Magazine, the trio seemed fine together, although Jay Z sat by a firepit while Beyonce and Solonge – clad in her peach Phillip Lim dress – danced with Naomi Campbell.
They did, however, leave ‘abruptly’ the magazine reports.
Both women seemed merry but weren’t pictured holding alcohol.
Solange has admitted to issues with drugs in the past, and cancelled her European tour last year amidst rumours of usage… according to Radar Online.
In February, 2009, she tweeted about ending up in the hospital after a Nyquil overdose.
‘I don’t even smoke weed that often, but I’m finding I can’t remember things,’ she revealed on Twitter on Septemer 1 the same year.
Solange and the music mogul have been close for over a decade, with Jay Z – real name Shawn Carter – taking a big brother style role to the fledgling star after he started dating her sister.
Beyonce and Jay Z were famously friends first but started a relationship way back in 2001, they then married in 2008.
Mrs Carter is extremely close to her younger sibling, and made a surprise appearance at Coachella this year to support Solange’s set at the California music festival.
Back in 2008, she said: ‘People think there should be this great rivalry between us, but there’s never been any competition.
‘There’s a big age gap and we are two very different characters.
‘I try to stand on my own two feet and not talk too much about my sister. But the two of us are still close.’
She even said when asked if Jay Z was an inspiration: ‘I know. I have a lot of people to look up to and learn from.’
Always in Beyonce’s shadow despite her own immense talent, Solange had a few stints in Destiny’s Child, before signing with her father’s Mathew’s Music World Entertainment label; he and he girls’ mother Tina had quit their jobs to focus on their eldest child’s career.
But it paid off for Solange initially, too, as her her first studio album Solo Star – released when she was just 16 in 2003 – was a quiet success.
Just a year later, however, she married Daniel Smith, and after giving birth to their son Daniel Julez J. Smith Jr, moved to Idaho, where she occupied herself with writing music for her sister and ex Destiny’s Child stars Kelly Rowland and Michelle Williams.
But she missed the buzz of performing herself and after divorcing Smith in 2007, Solange threw herself back into the fray moving to Los Angeles so she could begin to start recording her own material.
It paid off as her second album, Sol-Angel and the Hadley St. Dreams, hit No. 9 on the Billboard 200 and garnered positive reviews.
She set up her own label, Saint Records, and recorded the album, True, in 2012 and has plans for a follow up later this year.
While no Beyonce, Solange is recognised as fashion icon and her Motown songwriting roots are respected throughout the industry.
The formerly solid family was rocked in 2009 when the girls’ mother Tina filed for divorce from Mathew, who was then still Beyonce’s manager, after it emerged he’d fathered a child during an extra-marital affair with Alexsandra Wright.
The Crazy in Love singer singer later ended her business relationship with her father, and neither sister attended his wedding to Gena Avery last year. As a family unit, they’ve still remained strong it had seemed, with Solange mentioning frequently in interviews that her son Juelz and baby Blue are more like siblings than cousins. Daily Mail