Morgana does not pick up on the misspeak. Such a thing is not entirely uncommon for Gwen, and Morgana would never point it out. Also, she's turning over in her mind exactly when that event took place. "The North Country -- I do not recall --"

Then it hits her: "You are ahead of us." Because a statement like that needs to be explained, " Sometimes people who know each other, they come from different points in their life." She thinks of how the Doctor explained it to her.

"It is like going for a walk in the forest. If you went ahead of Arthur and I, for some reason, and we took another path altogether, with the three of us ending up in the same spot, eventually."

"How long has it been since Arthur," it's an event she would rather not recall, all the worry and fear of the near loss of the crown prince, "was attacked by the Questing Beast?" That would give her a better idea.