My Kingdom for a Quest

Arthur is the rightful king of Briton, but his Uncle Mordreth refuses to give up the regency. Arthur and Grandfather are now returning with allies to wrestle the kingdom from his uncle's grasp. But not all is as it seems among his allies, and everyone has secrets. New loves, old loves, lost loves, kingdoms conquered and kingdoms stolen. Who is the real "rightful heir" and will the nearly forgotten sword in the stone finally answer this question?