Board Thread:Spoilers!/@comment-26901329-20150728074242/@comment-24674051-20150814144624

Back on topic. Part of the description of the character (if we can believe it) is that he is a man-servant. That would be someone like a Valet or a Butler (most likely). So that description would rule out any knights, or family members related to Arthur (of which Mordred is both).

And as I previously pointed out, this does not have to be related to Camelot at all. Others have suggested a previous Dark One. And I am inclined to beleive that.