From The Stargate Omnipedia

Queen consort of King Arthur. Guinevere was likely a human from Earth, who served as the basis for the Arthurian myth.

Merlin, who had once known Guinevere during his days on Earth, later mistook Samantha Carter for her after thawing from an Ancient stasis unit.


The Quest, Part 2 - After a thousand years in an Ancient stasis unit, Merlin emerges believing he is surrounded by his old friends.