Nimueh made sure it stayed a secret.
That she was there in Uther's youth. When he was bold and open and full of equal parts cockiness and sweetness.
Before Ygraine, Nimueh was there. They travelled together, far from Uther's home, doing the great deeds that would make men speak Uther's name for decades.
But Nimueh ... she was not the marrying sort. She adored him then. But she didn't want to keep him.
And Ygraine, who was like a sister to her, was madly in love with him; she had been since Nimueh first introduced them. And so it was no hard decision to choose Ygraine over Uther. They were a better match. And Nimueh's generosity was always her great fault.
And so it was with kind intentions that Nimueh cast the spell that drew out those parts of Uther's mind, those parts that remembered his care for her, his infatuation with her. And the hundred nights they spent riding under the moon, fighting side by side, making love in fields and haystacks and clearings in the woods, they seeped out of Uther's head like ink or tar. Memories, thick and hot. Leaving behind nothing but a vague memory of solitary travel, so that now, in Uther's mind, Nimueh was nothing more than that curious friend of the lovely young Ygraine.
Many years later, whenever Uther tries to kill her - or vice versa - she wonders if it would have been different if she had left him just a few of those nights to dream about, to remember. If it would temper his rage, his disgust, if it would restrain the way Uther looked at her as if she were empty of feeling or faithfulness or anything human. Like she was a snakeskin stuffed with poisoned straw. Would he look at her differently if his mind's eye could still see her eyes darken as she slid her body onto his? Would he look at her bare shoulders above the neckline of her dress and remember the taste of her neck on his lips? Would he think - if only briefly - of something other than killing her, she wondered.
She could bring his memories back now, of course. But it would only make his loss sharper, let him play the victim of magic once again, to rail once again at the dangers of power man beings who play with people's lives. And though at times she felt Uther deserved to be destroyed, there was surely no use tormenting him so that his wrath would rain down on all magical beings, most of whom were far less able to protect themselves than she was.
But sometimes she wonders about how she and Uther ended up on their particular battlefield. She wonders why she didn't think twice about erasing herself from his world.
She wonders if maybe, on that day, she herself forgot that magic always costs.
Author's notes: Written for the livejournal community comment_fic. Prompt was Uther/Nimueh, "Before Ygraine, Nimueh was there."