According to a new and, more importantly, unauthorised book based on Beyoncé, the trigger in question was indeed Rihanna, although not for reasons first expected.
"Solange has always been Beyoncé's biggest protector"
The shocking incident, which can be relived in full in the video below, may have been caused by elevated emotions after Jay Z expressed his desire to party with the 'Pon de Replay' singer.
Now, two things to point out - firstly, there was of course paparazzi induced speculation to the same effect around the time of the incident, so this isn't exactly fresh of the press.
Also, the book itself doesn't even fully back this up, and is merely speculating. Call us old fashioned, but we think it's a poor attempt to shift copies of the biography, Becoming Beyoncé, written by celebrity profiler J. Randy Taraborrelli.
In the book, Beyoncé is said to have told Jay Z in no uncertain terms he couldn't dance the night away under Rihanna's umbrella.
"It was a whispered married couple's argument that would have gone by completely unnoticed had not Solange overheard it.
"Solange has always been Beyoncé's biggest protector."
"[Beyonce and Jay Z] actually spent a year apart"
Taraborrelli certainly has previous form, having crafted a literary career by publishing biographies on a range of celebs, including the Hiltons, Marilyn Monroe and Michael Jackson.
In an interview with Entertainment Tonight, the celeb journalist also claimed that rumours about an affair between Jay Z and Rihanna were all part of a huge PR stunt, designed to boost the singers profile before her first single - as a result, the couple then went on a secret separation for a year.
"Beyoncé didn't know what to make of this, and it actually ended up breaking them up for a time.
"They spent maybe a year apart from each other because Beyoncé just wasn't sure of what to make of the situation with Rihanna."
Beyoncé herself has teased fans, with the lyrics to her Flawless remix, which states:
"Want me to come around and give you good karma, but no
We escalate, up in this bitch like elevators
Of course sometimes sh*t go down
When it's a billion dollars on an elevator"
Who really knows the truth, other than those who were actually in the elevator that night?
One thing I do know, though, is that a journalist conveniently promoting a new book release probably isn't the most reliable source...