After Lucerys Velaryon was killed by Aemond Targaryen, Lucerys's stepfather Daemon Targaryen hired two assassinates to kill Aegon's and Helaena's children, Blood and Cheese. Blood was a former Goldcloak and Cheese was a rat-catcher who knew all the sewers around King's Landing. This meant that they both had perfect recognition of the layout of the Red Keep. After breaking into the royal apartments, they found Helaena putting her children to bed. They demanded a son for a son. Helaena pleaded that kill her instead, but they refused. She named her younger son 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 to 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 had came, the Queen was cradling her son's body. Jaehaerys' death would eventually led to his mother's insanity and suicide.
In the books Edit
Blood was an serjeant in the City Watch. He lost his gold cloak for beating a whore to death whilst in a drunken rage. He spent time in Flea Bottom. After the death of Prince Lucerys Velaryon, Blood, along with Cheese was employed by Mysaria, Prince Daemon Targaryen's spymaster, to slay one of Aegon II Targaryen' sons.
Once Blood and Cheese confronted Queen Helaena Targaryen in the Tower of the Hand they told her to name which son she wanted them to kill. Helaena offered herself but they refused, stating it had to be a son. Although Helaena eventually named her youngest son Maelor (after Cheese threatened that Blood would rape her daughter Jaehaera if she did not choose one now), they killed Jaehaerys instead. It was Blood who slew Jaehaerys, striking the boy's head off with a single blow. After killing Jaehaerys, Blood and Cheese did no further harm to Helaena or her surviving children and fled with the prince's head in hand.