[Movie] Merlin (S1E09) Excalibur
Synopsis: The Black Knight arrives to interrupt Arthur’s coming-of-age celebrations and throws down the gauntlet to any knight who will fight him. He kills them all one by one. Gaius discovers that he is Uther’s dead brother-in-law, summoned from the grave by the witch Nimueh.
He is seeking revenge for the death of his sister, who died giving birth to Arthur by way of magic from Nimueh. Merlin learns from the Great Dragon that only a special sword (Excalibur), burnished with the Dragon’s fiery breath, can kill the knight.
The Dragon warns Merlin that only Arthur can wield it. Arthur is next to fight the Black Knight, but Uther takes Excalibur and faces the knight himself, slaying him in the end. Now that the sword has been wielded by someone other than Arthur, it is capable of being used for evil; to prevent that, the Great Dragon instructs Merlin to hide Excalibur far from the reach of mortal men.