Born in 109 AC to King Viserys I and Queen Alicent Hightower, the only daughter of that marriage and the king's second daughter overall. She was plumper than most of her house and less striking, but a pleasant and happy girl whom all agreed would make an excellent mother. By eleven she was a dragonrider on Dreamfyre, the she-dragon who had carried Rhaena Targaryen a century before, and the sky was said to be her greatest joy. In 122 AC, at thirteen, she was married to her elder brother Aegon after the ancient custom of their house, and barely a year later bore the twins Jaehaerys and Jaehaera, with Maelor following in 127 AC. The smallfolk of King's Landing loved her. On the last night of her father's life she brought all three children to his chamber, where the dying king told them a tale of their great-great-grandsire.
Her husband was crowned in the Dragonpit in 129 AC and her mother set a crown on her head and called her "my queen". When Aegon raged for Rhaenyra's execution it was Helaena, with Alicent and Grand Maester Orwyle, who argued for terms instead, and the king reluctantly sent Orwyle to Dragonstone under a peace banner. Then Aemond killed Lucerys Velaryon over Shipbreaker Bay, and Daemon promised Rhaenyra a son for a son. The men called Blood and Cheese knew that Helaena brought her children to her mother's rooms in the Tower of the Hand every evening before bed. They waited there, killed the guardsmen and barred the door, and made her choose which of her sons would die. She offered herself instead and was refused; threatened with worse for her daughter, she named Maelor, the youngest, as too small to understand what was being said of him. They killed Jaehaerys in front of her, took his head, and left her screaming.
She never recovered. She would not eat, would not bathe, would not leave her chambers, and would not look at Maelor, knowing what she had said. She and Aegon slept apart from that night on, and after Rook's Rest left him burned and broken she did not go to him once. She became useless as a dragonrider and could not be sent into battle. When King's Landing fell to Rhaenyra in early 130 AC she was taken captive, and some months later, a few days after the Battle Above the Gods Eye, she went out the window of her room in Maegor's Holdfast and died at once on the spikes below, aged twenty-one. In that moment Dreamfyre snapped two of her chains and roared until the Dragonpit shook. Why she did it is still argued over: Mushroom's tale of the Brothel Queens, Munkun's hangings on the castle wall, Eustace's claim that Mysaria chose that night to tell her how Maelor had died, and Gyldayn dismisses all three. By nightfall the city was saying she had been murdered, and King's Landing rose in riot crying justice for the beloved queen and her dead sons; Dreamfyre was killed when the mob stormed the Dragonpit. Her daughter Jaehaera went from a window of the same holdfast in 133 AC, ending the line of Aegon II and of Viserys I both.