Merlin revealing his magic is definitely going to be the ultimate test for Arthur and Merlin, and I think it might be explored in the fifth season,” Morgan says. “The levels of trust between friends is one thing, but Arthur’s distrust of magic is something that runs longer than he and Merlin have been friends. It will take much more influence and much more work to break and to overcome. Certainly we’re entering into that territory, but it’s never going to be an easy task for Merlin. Still, it has to happen sooner or later.
That the latter [Arthur] was entirely a fictitious person is difficult to believe. There is always some substratum of truth on which the wildest legends are based, though it may be so disguised and perverted as hardly to be recognized; and I do not hesitate to receive the Arthur of Nennius as the historic Arthur.