A source (not 50 Cent) tells the New York Daily News that Solange Knowles' infamous elevator attack on brother-in-law Jay Z happened after Jay made plans to head to Rihanna's Met Ball after-party without bringing Beyoncé.

The tension between the two started earlier in the night, when a group of Solange's "non-famous" friends reportedly crashed the gala and started dropping Jay Z's name.

"They were pretending they were guests of his and not hers. Management went to Julius (Beyonce's bodyguard) and said there's a problem," the source said.

Shortly afterward, Jay Z apparently confronted Solange and told her "don't use my name."

At that point, Solange decided she wanted to leave, another source told the Daily News, and Jay Z decided to take off for Rihanna's party on his own, calling ahead to say he wouldn't need extra security.

Solange reportedly lost it. Here's the second source's account of the conversation that took place in the elevator video:

"She said, 'Why can't you go home?' and to Beyonce 'Why does your husband need to go to the club right now?'"

"You're one to talk," Jay replied.

That's when the punching, kicking, and purse-swinging started.

Jay Z, Beyoncé, and Solange have yet to comment on what happened that night, but the sisters have been subtly throwing shade at each other on Instagram since then.

[Photo: AP Images]