"like the adulterous Guinevere in the Morte d'Arthur, she would be sentenced to be burnt at the stake and with no Lancelot to rescue her "
Arthur's Tomb - The Last Meeting of Lancelot and Guinevere. Artist Dante Gabriel Rossetti (1828-1882)
Public DomainArthur's Tomb - The Last Meeting of Lancelot and Guinevere. Artist Dante Gabriel Rossetti (1828-1882) - Credit: Wikimedia Commons

 Thomas Mallory's Morte d'Arthur recounts how Lancelot, the most trusted knight of legendary King Arthur, and Guinevere, Arthur's wife, are discovered in an adulterous affair.  Lancelot flees for his life and Arthur is forced by his own laws to sentence Guinevere to death by burning at the stake. 

Lancelot rescues Guinevere at the last moment, but in so doing divides the loyalties of the Knights of Camelot.  He flees to France,  and Arthur follows seeking revenge, leaving Guinevere in the care of Mordred, who then attempts to marry Guinevere himself.  Hearing of this treachery by a trusted knight, Arthur returns to do battle with Mordred, but he is fatally wounded in the process.  The last time Lancelot and Guinevere meet is at the tomb of the dead King Arthur, after which Guinevere takes herself off to a nunnery.