Queen Guinevere was the only thing in Cam'lod'n that John F. Kennedy found resembled the romanticized Arthurian legend. Kennedy immediately decided he'd try to lay her. She was receptive, and arranged a tour of the castle, until they were able to find a private moment.
While in mid-act, Merlin entered the room to announce he found a way for Kennedy to return home. When Merlin, horrified by what he was seeing, attempted to refuse to help Kennedy, Guinevere intervened, ordering Merlin to help Kennedy, and promising that if he didn't, she'd tell Arthur that Merlin had touched her inappropriately. Merlin relented, and sent Kennedy home.