HBO's Game of Thrones is infamous for its weddings. While some capture the royal splendor, things almost always go wrong for either the guests or the ones getting married. The Red Wedding is a glaring example of Game of Thrones' tragic weddings, and the one after that - the Purple Wedding keeps on with it. The reason why most weddings on Game of Thrones don't end well is simple: Westeros is a dangerous place where politicking takes precedence over everything else, and marriage is merely a political institution. The head of one such Great House of Westeros, Lord Tywin arranged marriages to strengthen House Lannister, and this practice ended up hurting the interests of his enemies.
Had Edmure Tully's wedding to Roslin Frey ended well, the Starks of Winterfell would have allied with the Freys of the Twins. Robb and his army would have likely taken Lord Tywin's home, Casterly Rock, and the War of the Five Kings would have taken a new turn. However, Lord Tywin prevented that from happening, as he collaborated with the host, and bride's father, Lord Walder Frey who then orchestrated the massacre of Robb Stark and his host at Edmure's wedding feast. Game of Thrones season 3, episode 9 "The Rains of Castamere," colloquially known as the Red Wedding was a big win for the Lannisters; the Purple Wedding, on the other hand, hurt their interests.
Prelude to the Purple Wedding
Though Joffrey is promised to Sansa Stark, he discards her for Margaery Tyrell in Game of Thrones season 2, episode 10 "Valar Morghulis." This development takes place after Joffrey's grandfather, Lord Tywin wins the Battle of the Blackwater for him. Stannis suffers a defeat as Petyr Baelish allies the Lannisters with the Tyrells. Joffrey names his grandfather the Hand of the King, and Lord Baelish is granted the castle of Harrenhal. Loras Tyrell presents his sister, Margaery to Joffrey who then sets Sansa aside. And so, King's Landing prepares for Joffrey and Margaery's wedding.
Petyr Baelish/ Littlefinger has tricks up his sleeve, and now that he is surrounded by the Tyrells, he knows what to plot next. In Game of Thrones' Valar Morghulis, he promises to help get Sansa home but doesn't reveal his cards. The Lannisters begin to think they have a claim on the North, as Tywin arranges Sansa's marriage to his son, Tyrion. With two successive victories and a Lannister-Stark union in place, everybody in the capital now looks forward to the extravagant royal wedding.
Joffrey Baratheon's Poisoning
The wedding takes place in Game of Thrones season 4, episode 2, "The Lion and the Rose." Joffrey weds Margaery in the Great Sept of Baelor, and the attendees include Cersei Lannister and her son, Tommen Baratheon, Lord Tywin and Jaime Lannister, Lord Mace, Lady Olenna, and Ser Loras Tyrell. Oberyn Martell and his paramour, Ellaria Sand, Sansa, and Tyrion Lannister are also present. Margaery's grandmother, Lady Olenna barely smiles, while Sansa rolls her eyes and declares, "We have a new queen." The Tyrells pay their share in the wedding since the crown is in the middle of the War of the Five Kings and the Iron Bank will have its due.
In Game of Thrones' "The Lion and the Rose," Lady Olenna walks up to Sansa at the wedding feast and offers her condolences. She fidgets with her plaits, and necklace as she says, "War is war, but killing a man at a wedding, horrid. What sort of monster would do such a thing?" Olenna also removes a vial of poison from Sansa's necklace, who's oblivious to the whole scheme. She leaves her with an interesting comment, "As if men need more reasons to fear marriage," and invites her to Highgarden. Joffrey appears bored at his wedding feast, while Margaery gets vicarious embarrassment from his actions.
The real drama begins when the pompous king has several imps reenact the War of the Five Kings. Sansa sits at the high table in sullen silence and Olenna shows disgust. Joffrey mocks his uncle, Tyrion Lannister, and hears a thinly-veiled insult in response. He pours wine over Tyrion's head and orders him to be his cupbearer. He has Tyrion fill his goblet, or some such at which point Margaery tries to distract him with their wedding pie. Just as Sansa and Tyrion are about to leave, Joffrey orders his uncle to serve him more wine. He takes a few more gulps and starts to cough, alarming everyone around him.
Baelish And Olenna's Machinations
The purple-faced Joffrey dies in Cersei's lap, and Dontos Hollard spirits Sansa from King's Landing. Mass panic and confusion grip the guests and Joffrey slowly raises a finger at Tyrion, who is inspecting the goblet in sheer disbelief. Cersei blames him for poisoning her son and orders her guards to seize him at the Game of Thrones season 4, episode 2's end. Tyrion is a prisoner of his own family - the ungrateful lot he saved during the Battle of the Blackwater. In Game of Thrones season 4, episode 3, "Breaker of Chains," Dontos Hollard ushers Sansa onto a ghost ship, in Baelish's care. After having his men shoot Dontos dead, Baelish removes Sansa's necklace, crushes one of its stones, and admits he had it made a few days ago.
Sansa wore the necklace to Joffrey's wedding as Ser Dontos had lovingly presented it to her as his family heirloom. A few seasons down the line, in Game of Thrones season 7, episode 3 "The Queen's Justice," after Jaime leads the sack of Highgarden, Olenna confesses to him her role in poisoning Joffrey:
I'd hate to die like your son. Clawing at my neck, foam and bile spilling from my mouth, eyes blood-red, skin purple. Must have been horrible for you, as a Kingsguard, as a father. It was horrible enough for me. A shocking scene. Not at all what i intended. You see, I had never seen the poison work before. Tell Cersei, I want her to know it was me.
Not only does the Purple Wedding end Joffrey's reign, but it also paves the way for other key Game of Thrones incidents, such as the Mountain vs. the Viper, Tywin's death, and Margaery's marriage to Joffrey's younger brother, Tommen among others.