Disclaimer: Melinda Warren isn't mine, though Morgaine, Azar, their son Aidan, Melinda's daughter Claire, Juliet Calloway, and Catherine Morgan are.
Prologue: Morgaine knew she should have asked her sister to join her when she went to fight Azar, but she was young and proud, and she wanted to prove to her powerful older sister that she was a strong witch as well. But when the demon overpowered her and forced himself on her, leaving her for dead in an alley, she knew she'd been a fool. She called out with her mind for Melinda, even as despair and pain ripped her apart.
She didn't die that night, and soon her belly grew round with child, the child of a witch and a demon. Morgaine stood at her window, a hand on the curve of her stomach, thinking about the choice she'd made. She knew it was the right choice, but she knew no one would agree, especially Melinda.
"Sister," Melinda said as she walked into Morgaine's room, "I have the potion." Melinda had brewed a potion to kill Morgaine's unborn child.
"I won't need it," Morgaine said softly.
"What? Morgaine, you cannot be thinking of allowing the child to be born! It is demon get, and evil by blood!"
"Blood is not everything, and in any case, he also has my blood. I will raise my son to use his powers for good. What a victory over evil, to use powers born of darkness for the light."
"This is madness. Morgaine, you will have other children. This one is not truly yours. You must destroy him now."
"Then you allow evil to be strengthened by giving it another warrior. If you would do this, then you too are evil, and no sister of mine."
Both sisters' eyes were filled with tears, but neither allowed a single tear to spill over. Morgaine stared into her older sister's eyes for a moment, before lifting her chin in defiance. "Very well. Then I shall leave, and trouble you no more." She brushed past her sister and walked out of the house. Melinda made a movement as though she wanted to reach out to her sister, but she thought better of it.
Twelve years later, the sisters met again, in the depths of a wood in the colony of New York. There were no witnesses, so no one ever knew exactly what occurred during that meeting. But all knew that there was some great battle of magical power, and at the end of it, both sisters lay dead. Back in Virginia, Melinda's daughter Claire Warren received the news with a composed face. But in New York, Aidan Warren felt fury course through him, driving him to a vow. He vowed that he and his descendants would forever be the enemy of Claire and her descendants. He changed his name to Aidan Morgan, in honor of his mother, and he taught his children to hate and fear the Warrens.
For 100 years, the two clans caused each other harm whenever possible, betraying one another to witch hunters, sending demons to each other, even occasionally committing outright murder. Finally, though, Astrid Halliwell decided things had gone too far, and she sent a message to Catherine Morgan. The coven leaders met in Philadelphia, with a neutral fellow witch, Monica Calloway. There they decided to end the fighting. There was no truce, merely a ceasefire. The two families would simply ignore each other. They would never help each other, but would also never directly harm each other. But as Monica performed the ritual to seal this agreement, she froze, caught by a vision. When she came out of it, she said, "This settlement shall not last. The prophecy of Melinda Warren has been split between both families, and one day, both sides shall receive a Power of Three. These children must reunite their lines, or this world shall end. Only when the clans are joined once more will we be saved."
Astrid looked at Catherine, bemused. "So, our families will be one again, someday."
Catherine gave her an ironic smile. "Yes, someday. But today is not that day." And then she left.
So the agreement held, and it worked. The Morgans never forgot the prophecy of Monica Calloway, but the Halliwells eventually did. So when Monica's vision came to pass, only one side was expecting it, though the other was soon to be told...
A/N: I know Melinda died at the stake, but let's just say she didn't. This is an AU, after all. R&R!