Doctor Strange #31 (1978)

Flying over the Atlantic on pressing business, Doctor Strange's astral form arrives in fabled Atlantis. Forcing his way into Namor's throne room, where he warns the Sub-Mariner of a threat to his life. When the Sub-Mariner scoffs at this notion, Strange shows him an image of Alaric, a being who has seized ownership of the ancient Atlantean artifact, the Sword of Kamuu. With this sword, Strange explains, Alaric can gain immortality by using it to slay the Sorcerer Supreme. As the Sub-Mariner's ancestry is linked to the sword, he had come to Atlantis seeking the undersea monarch's aid. Namor is at odds about leaving his kingdom however, when Strange is suddenly struck with a bolt of pain -- signaling Alaric's arrival in New York City, Namor agrees to travel there to help the endangered sorcerer. Alaric appears in New York and travels quickly to Dr. Strange's Sanctum Sanctorum where he easily slashes through the mystical barriers that protect the place from intruders. There he finds Clea protecting the unconscious body of Dr. Strange. Although Clea proves to be no match for Alaric, who easily defeats Strange's apprentice and lover, the delay allows Strange enough time for his astral form to return to his physical body and defend himself from Alaric. As the two battle, Strange can only keep Alaric on the defensive, until the Sub-Mariner arrives having decided to aid his friend after all. The addition of Namor's physical might delays Alaric even further, and when Alaric strikes Namor he enacts the the Curse of Zartra. The curse causes anyone who strikes a member of the Atlantean royal family with the Sword of Kamuu would meet their own end and finds himself severely weakened enough for the revived Clea to trap him in Dyzakk's Cage. With the threat over, the Sub-Mariner takes possession of the sword, and Dr. Strange goes to Clea's comfort.