From A Wiki of Ice and Fire
The Purple Wedding is the fan-given nickname for the wedding between King Joffrey Baratheon and Margaery Tyrell in 300AL. The wedding is a lavish affair, but ends in disarray when Joffrey dies after drinking poisoned wine. Unlike the Red Wedding, this wedding is not called so in the books.
After House Tyrell allies itself to his reign, King Joffrey Baratheon discards Sansa Stark and is betrothed to Margaery Tyrell. Her grandmother, Olenna Tyrell, questions Sansa about Joffrey to see if the stories of the boy king's cruelty are true. Instead of Joffrey, Sansa marries the king's uncle, Tyrion Lannister.
The marriage of Joffrey and Margaery occurs at midday on the first day of the new century, 300AL, in the Great Sept of Baelor, before statues of the Father and the Mother. The High Septon performs the ceremony.
The wedding feast takes place in the throne room in the Red Keep. Seventy-seven dishes are planned for the dinner. Hamish the Harper is the first performer, premiering "Lord Renly's Ride" and also singing "A Rose of Gold", "The Rains of Castamere", "Maiden, Mother, and Crone", "My Lady Wife". Hamish is followed by a trained bear and Pentoshi tumblers. Collio Quaynis sings "The Dance of the Dragons", a song of the Doom of Valyria, "Bessa the Barmaid", and another version of "The Rains of Castamere". The fools Moon Boy, Butterbumps, and Dontos Hollard also perform for the guests. Further entertainment comes from pyromancers, pipers, trained dogs, sword swallowers, and a juggler. Galyeon sings a song of the Battle of the Blackwater with seventy-seven verses. Dancers from the Summer Isles also perform during the wedding feast.
Tyrion is seated several seats away from the other Lannister attendees along with Sansa. Joffrey, while drunk, continually attempts to provoke his uncle, who is a dwarf. A pair of dwarf jousters enter the throne room atop a dog and a sow and proceed to mock the Starks and Joffrey's Baratheon uncles; Joffrey encourages Tyrion to join them. After Tyrion refuses and embarasses the boy king, Joffrey empties the large royal chalice of wine over his uncle and orders him to be his cupbearer. Alaric of Eysen is scheduled to perform, but the great ceremonial pie arrives, served by six cooks. Ilyn Payne cuts the pie, allowing doves to fly free from it.
At some point during the feast, Joffrey's wine is poisoned. After deeply drinking wine from the wedding chalice, and eating several handfuls of the pie, Joffrey begins to cough, each one more violent than the last. Chaos descends upon the feast, as guests struggle to get out. The knights Garlan Tyrell, Meryn Trant, and Osmund Kettleblack run to the aid of Joffrey while the court scatters, some fleeing and others looking on. Joffrey points at Tyrion in his dying moments; Tyrion empties the remainder of the chalice on the floor. After Joffrey is confirmed dead, his mother, Cersei Lannister, orders the arrest of Tyrion and Sansa.
The murder of Joffrey is revealed as a murky plot organized by the Tyrells and Petyr Baelish, but Tyrion and Sansa are falsely implicated. The poison is the Strangler, smuggled into the feast in the hairnet of the unsuspecting Sansa.
With the exception of his mother, Cersei, Joffrey is not particularly mourned by anyone; even his biological father, Jaime Lannister, feels that Joffrey deserved his fate. Tyrion states that Joffrey would have become a worse king than the Mad King. Arys Oakheart thinks that the only good thing that could be said of Joffrey was that he was tall and strong for his age.
The wedding of Joffrey and Margaery has been dubbed the Purple Wedding by fans for various reasons. The poison used to kill Joffrey is smuggled to the wedding in the purple amethyst hairnet of Sansa Stark, while the wine the king drinks is described first as dark red and soon after as purple. Joffrey's face turns red and then darker as he chokes from the poison. Purple is also a color often associated with royalty.
|“||The northern girl. Winterfell’s daughter. We heard she killed the king with a spell, and afterward changed into a wolf with big leather wings like a bat, and flew out a tower window. But she left the dwarf behind and Cersei means to have his head. ||”|
|“||Weddings have become more perilous than battles, it would seem.||”|