Mitchell says that Vala's pregnancy is similar to how King Arthur was conceived and born. In reality it isn't even close. King Arthur was concieved after his father, Uther Pendragon met and fell in love with Arthur's mother Igrane. Igrane was married to Gorlois The Duke of Cornwall at the time. Uther went to war against Gorlois and while the Duke was being killed Uther had Merlin cast a spell on him (not Igrane as Mitchell said) to make him look like Gorlois he then entered Tintagel (Gorlois' castle) and seduced Igrane when he left she was pregnant with Arthur.