Prelude to the Council
King Daeron II's heir, Prince Baelor Breakspear, had perished in an accident during a Trial of Seven in 209 AL, leaving his eldest son Valarr to inherit the crown. However, later that year the Great Spring Sickness killed King Daeron and both of Baelor's sons, Valarr and Matarys. This in turn left Daeron's second son Aerys I to inherit. Aerys left no issue, and upon his death in 221 the crown was passed to his youngest brother, who reigned as King Maekar I, the fourth son of King Daeron II. At the death of Maekar at the hands of a rebellious lord in 233, a council was convened to decide who would inherit the Iron Throne since both of Maekar's eldest sons were dead and their inheritors were only children.
Maekar's oldest son, Daeron, called Daeron the Drunken, was a dissolute whore-monger who had died of a sexually transmitted pox, and left only a feeble-witted daughter as a possible heir. His second son, Aerion Brightflame, was a cruel madman who had died in 232 as a result of drinking wildfire in the mistaken belief it would turn him into a dragon. Aemon and Aegon had not expected to inherit the throne with two grown sons ahead of them. Aemon was already a chained maester serving at his brother Daeron's castle.
The council decided to bypass Daeron's daughter and Aerion's son and first quietly offered the throne to Aemon, who declined the invitation. They then chose Aegon, who was crowned as Aegon V, the fourth son of the fourth son of Daeron II, earning him the name Aegon the Unlikely. Aemon joined the Night's Watch to prevent others from using him against his brother.