Jaehaerys II Targaryen, the second of his name, was born in 225 AC, the second son of King Aegon V the Unlikely and his queen Betha Blackwood. Slight and sickly all his days, short of breath and frail of body, he was never the equal in vigor of his brothers, yet he proved sharp of mind and strong of will. His father, who had let his own children wed for love, nonetheless tried to bind the next generation to the great houses with betrothals, but in 240 AC Jaehaerys defied those plans and eloped with his own sister, Princess Shaera, restoring after a long lapse the old Valyrian custom of marriage within the royal house. Of that union came a son and a daughter, Aerys and Rhaella.
A prophecy shaped the marriages he in turn arranged. A woods witch, the friend of Jenny of Oldstones, had foretold that the prince that was promised would be born of the line of Aerys and Rhaella, and so Jaehaerys wed his two children to one another, binding brother to sister once more in the hope of that promised savior. He had not looked to be king, but in 259 AC the Tragedy at Summerhall took his father King Aegon V, his elder brother Prince Duncan the Small, and the aged Lord Commander Ser Duncan the Tall together in a single fire, and the crown fell to Jaehaerys.
For all its brevity, his reign was reckoned a wise one, for the frail king chose able counselors and ruled with good sense. Its great event was the War of the Ninepenny Kings, fought on the Stepstones against the Band of Nine, who sought to set the Blackfyre pretender Maelys the Monstrous upon the Iron Throne. The host Jaehaerys sent under Lord Ormund Baratheon broke them; Ormund fell in the fighting, but in the thick of it the young knight Ser Barristan Selmy cut down Maelys in single combat, ending at last the male line of the Black Dragon that Aegon the Unworthy's bastards had begun. Jaehaerys outlived the victory by only a few years. His weak health failed him in 262 AC, after a reign of but three years, and the throne passed to his son, Aerys, the Second of His Name.