- "When the guards burst in, they found Queen Helaena still screaming, clasping her dead son's body to her, mad with grief. The blood of her children transformed a dynastic dispute into a war of annihilation."
- ―Catelyn Stark
During the Dance of the Dragons, Lucerys Velaryon was sent by his mother Rhaenyra Targaryen, to gain support from Borros Baratheon, who had declared for neither faction. However, Aemond Targaryen and Lucerys had arrived consecutively at Storm's End. However, Borros had already came to the conclusion that Rhaenyra was inferior to him, and banished Lucerys from the castle. However, Aemond wanted blood. On his way back to Dragonstone, Lucerys was caught in a storm above the fortress, and his young dragon Arrax could not take it. Aemond then rose to Lucerys' elevation on Vhagar, who was five times the size of Arrax. Vhagar bit into Arrax's neck so hard that she decapitated him. Arrax's lifeless body fell, with Lucerys on it, and he drowned in Shipbreaker Bay. Rhaenyra was unsure whether to end the civil war right there, but Daemon Targaryen said that Lucerys would be avenged with the death of Aegon II Targaryen's eldest son Jaehaerys Targaryen.
Daemon hired a former member of the City Watch, Blood, and a rat catcher of the Red Keep, Cheese, to murder Jaehaerys. This meant that they both had perfect recognition of the layout of the Red Keep. After breaking into the royal apartments, they found Helaena Targaryen putting her children to bed. They demanded a son for a son. Helaena pleaded they kill her instead, but they refused. She named Jaehaerys's younger brother Maelor as the victim. However, Cheese just told Maelor that his mother wanted him dead, and some believe that Helaena named Maelor because Jaehaerys was heir to the Iron Throne, or because Maelor was just too young to understand. This request became an act of defiance against the Greens, as Blood just beheaded Jaehaerys with a single blow. By the time the guards came, the Queen was cradling her son's body.
Jaehaerys's death would eventually led to his mother's insanity and suicide.
In the books
Rhaenyra collapsed when learning of Lucerys's death. Prince Daemon, at Harrenhal, sent a raven to his wife, promising that her son's death would be avenged.
Using one of his friends from King's Landing, Daemon enlisted the help of a former serjeant in the City Watch, known now only as Blood, and a rat-catcher from the Red Keep, known now only as Cheese. The two sneaked into the Red Keep, using secret tunnels and hidden doors, which brought them into the Tower of the Hand. There, Queen Alicent was bound and gagged, and her bedmaid strangled. When Queen Helaena and her three children appeared, Blood and Cheese barred the doors and told Helaena to choose which of her sons would die. Helaena reluctantly chose Maelor, but Blood did the opposite and killed Prince Jaehaerys instead. The two fled with the prince's head, leaving the others unharmed.