Picked this up at the Book Thing, for BC.

From the cover -
Arthur is King! But while he is unchallenged on the battlefield, sinister powers plot to destroy him in his own Camelot. When the rose-gold witch Morgause, Arthur's half-sister, ensnares him into an incestuous liaison - and bears his son, Mordred, to use to her own evil ends - a fatal web of love, betrayal, and vengeance begins...
Seen through the eyes of Arthur's prophetic protector, Merlin - whose own mysterious powers are in dire danger - here is a tale rich with the majesty and turbulence of the magnificent legend it tells... resplendent with Mary Stewart's own special magic.

I read this several years on a bookring. Comments from many readers, including myself are here.

RELEASE NOTES:

Left on the OBCZ shelf this afternoon.