I pretty much agree with everything you just wrote.
I think this will be one of the biggest character development moments for Arthur, on so many different levels... on a magic level (as someone mentioned - being what he has been taught to despise), and on an emotional level as well. After all, he is "responsible", in some sense, for the death of his mother - he's always known that his father misses her very much and sees his mother in him... but perhaps now he'll realise why it's always felt like his father has put so much pressure and "blamed" him.

I have a feeling Morgause will be Arthur's aunt - she doesn't look VERY young, and she does have Arthur's blonde hair. (tenuous link, I know. :D)