User blog comment:Merganafan23/Character ages/timeline/@comment-5102537-20120804234140/@comment-5364525-20120806171359

"She can only be Morgana's half-sister through her mother, otherwise Gaius, Morgause and Morgana would have thought that they were full sisters before Uther told Gaius that he was Morgana's father."

Very good point... I think I'm going to just assume that the inconsistencies are the result of an epic plot hole. It makes much more sense that Morgause is older than Arthur, but her back story is so vague as to drive my OCD crazy:)