The third head of the dragon

Prince Aegon—third son of Prince Baelon Targaryen, great-great-grandson and namesake of the great Aegon the Conqueror—was never meant to survive his first year. But the Gods, having laughed their fill at their own original designs, altered the fates of men in mere jest. Now, Viserys and Daemon Targaryen have a younger brother, in whom the realm sees the third head of the dragon from the royal sigil. What life have the Gods ordained for him? What mark will he leave upon the history of the Seven Kingdoms? — Description from novelcodex.org