A leaked security video from a New York City hotel reportedly shows Solange Knowles - sister of Beyonce - attacking her brother-in-law Jay-Z.
The footage, obtained by US website TMZ.com, was purportedly filmed in a lift at The Standard Hotel on the night the trio attended the Met Gala last week.
The video appears to show Solange attacking Jay Z in Beyonce's presence and a security guard - who presses a button to stop the lift - repeatedly intervenes. There is no audio on the footage.
Once outside the hotel, the sisters were seen getting into one car, while Jay-Z was directed to another.
The Standard Hotel issued a statement saying it is "shocked and disappointed that there was a clear breach of our security system".
The hotel says the leaked video violates the confidentiality it provides customers.
"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."
TMZ posted a longer, three-minute version of the video later yesterday. Representatives for Beyonce, Jay Z and Solange declined to comment.
Jay Z, 44, and Beyonce, 32, were married in 2008. They will kick-off their co-headlining On The Run Tour on June 25 in Miami.
Solange, 27, recently performed at the Coachella Valley Music and Arts Festival, where Beyonce joined her onstage.