Duel between Arthur and Lancelot's Shade

When Lancelot was resurrected as a Shade in league with Morgana, he enchanted Arthur's fianceé, Guinevere so that she will fall in love with him. Lancelot gave Gwen the bracelet, that night Guinevere cheated on Arthur by kissing Lancelot, Agravaine brought Arthur into the room and hell broke loose. Arthur attacked the Shade, but Lancelot fought back, they had a duel. When Lancelot gave Arthur a blow to make him vulnerable, Merlin stepped in and disarmed Lancelot, allowing Arthur to regain his strength and pick up his sword, ready to strike. But then Gwen stepped between the to break up the fight. Then Arthur had both Guinevere and Lancelot thrown in the dungeon (Lancelot du Lac).