The King of France was attending a masquerade ball, The Bal des Ardents, which translates as "The Ball of the Burning Men", which we hope was name after the event. If it was actually called that before it happened, then suspicions would have been aroused.
Charles VI was known for his awesome dance moves. That king could move. Think John Travolta on ice having an epileptic fit whilst holding seven octopi (or octopuses, or octopuddies) who are also having epileptic fits. Strobe lighting was very popular six hundred years ago. It was an issue.
The King of France, never wanting to miss an opportunity, decided to get up and dance. When shouts were heard from the spectators, "Yo, Kingy, You're On Fire!", Charles VI just assumed they were paying him compliments.
Little did he realise, he was actually on fire.
A torch had been brought into the event by his brother, Louis, Duke of Orleans. Now, we're not saying the King's brother had it in for him, but he really did. The two didn't get along. But, boys will be boys. What can you do?
Well, for starters, you can bring a torch into a packed area and set a few dancers on fire, hoping that fire would spread like, well, fire, and hope the king goes up like a roman candle. Pwoooof.
Although four of the dancers were killed, King Charles VI survived the ordeal.