It was the glorious festival collaboration that turned sour: Jay-Z and Justin Timberlake collaborated on tracks from Jay-Z's new album Magna Carta Holy Grail in a three day series of surprise performances and "I was there" moments. Sunday evening's performance approached and the 40,000-strong crowd of music fans waited for the joint headline performance that would serve as the cherry on top of a one-in-a-lifetime celebration of hiphop sounds. However, in currently unknown circumstances at 9pm two men were stabbed and had to be rushed to hospital where one is reportedly currently stable, yet one is said to be "in critical condition," according to Scotland Yard via BBC News.

Jay Z
Jay-Z Performed A Festival Set During Which Two Men Were Stabbed.

The attack occurred at approximately 21:00 BST in the midst of the crowd, many of whom were exultant in the presence of their musical heroes yet a select few will have had their evening's experience marred by the nightmarish attack.

Both men are believed to be in their twenties and the incident occurred in Queen Elizabeth Olympic Park in East London's Stratford where the 3-day event was taking place. After being alerted, festival medics and police forced their way through the teeming crowd crush to attend to the injured men, yet it is unclear whether the two stabbings are connected.

Justin Timberlake
It Is Unknown What Led To The Crowd Stabbing During Jay-Z & Justin Timberlake's Festival Appearance.

Neither Jay-Z nor Timberlake have commented on the incident as news that Jay-Z's latest studio album Magna Carta Holy Grail has hit the top of the UK charts has been announced, perhaps boosted by the rapper's guest appearance during Timberlake's Friday show, his own headline slot on Saturday and the duo's joint headline slot on Sunday night.

Jay Z
Jay-Z & Justin Timberlake Performed Three Times Together During The Weekend.

No arrests have been made yet as police attempt to piece together the events which led to the unsettling incident, and are appealing to witnesses to come forward and give evidence.