(But his wife shakes her head, looking at Igraine and Nimueh both. “I love you, both of you. Look after him.”)

The above is the only mistake I was able to spot--'looking at Igraine and Nimueh both' should be ''looking at Uther and Nimueh both''. Cause it was Igraine speaking- she wouldn't be looking at herself and talking to herself.

I thought the story was wonderful. The duality of the father and son history- Only Arthur getting it right where Uther wasn't able. (so far)
It was a very enjoyable read. Thanks for sharing it.