Recently I came across a FANTASTIC series in which Merlin was the son of the Queen of Succubi, serving the the Kingdom of Mercia. In the first part, Arthur was a sex-slave given to Merlin by his king. I remember bits and pieces, like Ygraine being alive and Morgana marrying King Bayard. Aaargh, it was so well done! I can't believe it hasn't gotten wider recognition/fame! Help me find it!
P.S. If the author is reading this, PLEASE post your amazing fic to AO3!