beyond the wide world's end

Well, those two, but something along the general lines of it not being Rilian who came back, but Rilian's son by the Lady of the Green Kirtle, or that it was Rilian that came back, but that he came back with a child, or that the son he had by his wife wasn't, but a babe found floating in a boat in the underground lake, Rilian's child by the Lady of the Green Kirtle -- variations on a story like that, so that by the time LB/Dust rolls around, it's a fairly well accepted story that the line of the kings of Narnia also bears a witch's blood.