Joffrey is poisoned at his wedding feast after marrying Margaery Tyrell in season four. Cersei immediately blames Tyrion and his wife, Sansa, who flees the Capitol in time with Ser Dontos to escape the queen's wrath. Unbeknown to Sansa, she did play a part in Joffrey's downfall. The poison that killed Joffrey was concealed in Sansa's necklace.
Before they can talk Joffrey back to his seat he wants more wine, and Tyrion gets a flagon from a serving girl and fills the chalice 3/4s of the way full. Joffrey takes a good sized hit on that but we aren't told the color of the wine at that point. Then he puts the chalice down on the table near Tyrion's seat. Ned is killed at the order of Cersei's tyrannical teenage son, King Joffrey Baratheon. Meanwhile, in Essos, the exiled Viserys Targaryen, son of the former king, forces his sister Daenerys to marry a Dothraki warlord in exchange for an army to pursue his claim to the Iron Throne. If Joffrey lives, Tyrion isn't accused of his murder, which means Tyrion doesn't kill Tywin. Tywin knew how crucial House Tyrell was to the success of the dynasty. As such he would have likely explained this to Joffrey, be it with words or a sharp lesson which is what he said Joffrey needed in the books. He said this to Tyrion, who thought to