User blog comment:It's Good to be the Queen/Pendragon Family Reunion/@comment-5102537-20121014172327/@comment-4623180-20121015004320

Fimber, I believe you're wrong that Arthur knows of the true circumstances of his birth. He went nuts when he "discovered" it in The Sins of the Father, and he expressed sympathy for all those with magic that he had executed. He told Uther how we he uses it to cover up is guilt. If he had discovered it again before Uther's death, he would have realised his father lied to him about not having lied to him, and he probably would've considered lifting the ban off magic! Well of course it'd be a bit different, with Morgana giving it a bad name.. so maybe not.. but I think the only big family secret Arthur found out since The Sins of the Father was that Morgana was his half-sister. But this was at a dire time and Camelot was in need. Uther also went broken after that so there'd be no point being mad at him, but no doubt Arthur would've (and we saw him sitting around moping) been depressed about that, and would've thought about it for years later.

So, Arthur does not know the true circumstances of his birth. It was such a big deal in The Sins of the Father, so why on earth would he not react if he found out later (it would be double the hatred, his father double-lied to him!)? Or more importantly, how? Knowledge doesn't just pop up.