Guinevere had an affair with a knight, Sir Lancelot.
Guinevere . In medieval romances , one of the most prominent story arcs is Queen Guinevere 's love affair with her husband 's chief knight , Lancelot . Sir Lancelot du Lac ( meaning Lancelot of the lake , baptised as Galahad ) was one of the Knights of the Round Table in the Arthurian legend .