The duel between Arthur and Lancelot's Shade occurred after Lancelot was resurrected as a Shade and was in league with Morgana and she enchanted a bracelet which Lancelot's Shade gifted to Arthur's fiancée, Guinevere, so she would fall in love with him again. Guinevere then met with him at night and Arthur, brought by Agravaine, saw them kissing each other. Arthur attacked the Shade, but the Shade fought back and they had a duel. When Lancelot's Shade gave Arthur a blow to make him vulnerable. Merlin stepped in and disarmed the Shade, allowing Arthur to regain his strength and pick up his sword, ready to strike. But then Gwen stepped between them to break up the fight. After that, Arthur had both Guinevere and Lancelot thrown in the dungeons (Lancelot du Lac).
Victory: Arthur Pendragon