The singer apparently “yelled at” Rachel during the Met Ball after party, which was being held at New York’s the Standard Hotel.
Interestingly, the magazine's sources have said that Bey - who appears to stand still throughout the video of Solange apparently attacking Jay Z - “got in the middle” of her disagreement with the designer.
Solange was previously pals with the designer and the pair even attended the 2012 Met Ball together.
Speculation over the cause of the altercation between Solange and Jay Z is growing, with one source reportedly telling Us Weekly that Solange was reacting to one of the ‘99 Problems’ rapper’s comments.
The couple and Solange are both yet to comment on the clip, though the Standard Hotel has released a statement explaining that they are “shocked and dismayed” by the “clear breach of our security system”.
TMZ's footage of the “attack” was filmed on the elevator’s security cameras and appears to show Solange physically attacking her brother-in-law until a security guard steps in.
Photos of Bey, Jay and Solange leaving the hotel moments after the incident show the rapper holding his face before getting in a car on his own, instead of joining Beyoncé and Solange in their vehicle.
Watch the video of the alleged attack below...