Maegor The Cruel

Maegor was five and ten years old when he married his half-sister in a Valyrian wedding ceremony performed by his mother, Queen Visenya. His bride wore her mother's luxurious, traditional Valyrian robes, though they were a little too big for her.
They were both raised together on Visenya's Dragonstone after Rhaenys's death in Dorne. Their father, Aegon, raised their brother, Aenys, in King's Landing, so the younger siblings knew only each other.
Even in his youth, Maegor was a rude child, loud and hot-tempered, known for throwing tantrums in the courtyard during training if he made a mistake or missed a parry. Nevertheless, Visenya's orders were clear: "Keep an eye on your sister."
Aegon and Rhaenys's daughter was small for her age, like her older brother, and slightly more frail. In her youth, she tended to Maegor, and then, following in the queen's footsteps, learned the intricacies of ruling the island of Dragonstone.
The young girl could often be seen sitting in the shade of the training yard, watching her brother and the royal guard train. On cold days, weakness forced her to remain in the castle, but watch through the window.
Maegor took his responsibilities more seriously than any other child his age, and this hardened him into the stoic man he was today, always keeping a watchful eye on his sister-wife. Ten years into their marriage, he still had no heir.
There was one place Maegor couldn't bring himself to go: no amount of training or battle could prepare him for the birthing chamber where his sister-wife now fought. Their third pregnancy agonized behind the half-open door, where he stood clutching his belt to hide his trembling hands.
"The baby won't turn, my prince, there's little we can do," the maester said as the sounds of her labor echoed down the hall. Maegor froze, his thoughts racing: watch her.
“Let me see her,” he finally said.