 Their now not-so secret affair is finally exposed by Guinevere's sworn enemy and Arthur's half-sister, the enchantress Morgan le Fay who had schemed against her on various occasions (sometimes being foiled in that by Lancelot, who had also defended Guinevere on many other occasions and performed assorted feats in her honour), and proven by two of King Lot's sons, Agravain and Mordred.Revealed as a betrayer of his king and friend, Lancelot fights and escapes.Incited to defend honour, Arthur reluctantly sentences his wife to be burned at the stake.