Purple Wedding

The Purple Wedding is an event in the War of the Five Kings. Mere hours after making their wedding vows in the Great Sept of Baelor during the wedding feast, King Joffrey is murdered via poison, by parties as of yet unknown.

Prelude
With House Lannister standing triumphant over its enemies after the Battle of the Blackwater and the Red Wedding, Joffrey is to cement his family's victory by marrying Margaery Tyrell, securing the support of the powerful House Tyrell.

During the feast, Margaery attempts to make a charitable gesture regarding the leftovers towards the poor (with Joffrey's approval) but Cersei, desperate to prove that Margaery has not removed all her authority as Queen, privately orders Grand Maester Pycelle to counter it. Tywin Lannister, meanwhile, has tense conversations with his counterparts Prince Oberon Martell and Lady Olenna Tyrell.

Joffrey introduces a mock play of "his" defeat of the rival claimants to the throne; all the players are dwarfs, so Joffrey mockingly tries to coerce Tyrion to join them. Tyrion carefully evades this demand, but at the same time deliberately insults Joffrey by subtly referencing his cowardice at the Battle of Blackwater; Joffrey, furious, stalks over and empties his wine goblet onto his uncle's head. His childish and sadistic actions are observed with increasing and obvious disgust by the guests, his mother and grandfather, and even his new bride.

Joffrey then declares he is thirsty and wants Tyrion to be his new cupbearer. He offers him the cup to fill, then drops it under the table, but Sansa picks it up for Tyrion; Tyrion fills it but silently refuses to kneel to Joffrey, prompting Joffrey to repeat the demand in increasing, petulant rage. Margaery distracts him by indicating the arrival of the traditional pigeon pie, and Tyrion sets the wine cup on the table; As Joffrey cuts the pie with his sword and shares some with Margaery, Tyrion and Sansa attempt to leave, but Joffrey calls them back and demands Tyrion bring him the cup again, as the dry pie is making him thirsty.

The Poisoning
After Joffrey takes a gulp, he starts coughing, but seems unconcerned for a moment. His coughing quickly grows so severe, however, that his throat closes and he cannot breath; Margaery notices and shouts that he is choking. Lurching forward, Joffrey falls to the floor. Jaime Lannister and Queen Cersei- his biological parents- rush to his side to aid him, but he continues to gag, as blood runs out of his nose and the color drains from his face. With his last strength, he attempts to point to Tyrion, seemingly believing him to be the culprit. Tyrion, meanwhile, has picked up the wine goblet and is attempting to sniff it for poison. The whites of Joffrey's eyes turn red, and he stops breathing.

Aftermath
In blind grief, the knee-jerk reaction of Joffrey's mother Cersei Lannister is to accuse Tyrion Lannister of poisoning the king. Tyrion is promptly seized by the Kingsguard.

In the confusion of Joffrey's death, Dontos Hollard calmly tells Sansa Stark to go with him if she wants to live. She relents.

In the books
In the A Song of Ice and Fire novels, the assassination of King Joffrey at his wedding receives no name, unlike the Red Wedding. The term "Purple Wedding" is a fan-term referring to the wine used to assassinate Joffrey and the fact that purple is a color associated with royalty; and, of course, to draw a parallel with the infamous Red Wedding. The nickname became so popular that even George R.R. Martin and the HBO production team have been known to use it. As Martin explained in an interview with TV Guide, "It's what the fans call the Purple Wedding, based on the color of the wine, which plays a big part."

His death is slightly different in the books. Instead of taking place outside the Red Keep, the wedding feast takes place inside the Red Keep itself, with Joffrey, Margaery and their families seated near the Iron Throne. In addition, Jaime doesn't return to King's Landing until shortly after the events. As Joffrey chokes to death, he claws repeatably at his throat in a desperate bid to get air, leaving bloody gashes.