User blog comment:Dragoon leGreat/The Disir- My Theory/@comment-4535687-20121027214952

That would explain why the Euchdag has said Arthur's bane is himself. In this case, Arhur doesn't allow magic to return and lets Mordred die (Aithusa saves him later, I think) making himself's bane because than Mordred feels betrayed and is going to kill Arthur.