In Merlin Season 5, Episode 3, "The Death Song of Uther Pendragon," Arthur unwittingly unleashes his father's vengeful spirit upon Camelot after using the magical Horn of Cathbhadh. The episode focuses on Arthur confronting Uther's disapproval of his reign and concludes with Merlin revealing his magic to the spirit, prompting Arthur to solidify his own ruling style by banishing his father. For more details, visit Merlin Wiki .