The Last Olympian
Percy and Luke (who is possessed by Kronos) battle at the top of Mount Olympus in the throne room. Luke is shocked back into his normal self when Annabeth reminds him of his promise that he would never harm her. The 'cursed blade' of the prophecy was the knife that Luke gave to Annabeth when he promises her that they are family. The Great Prophecy hinges on Percy's decision to give Luke the dagger rather than kill him. Luke commits suicide by stabbing himself in his mortal point when Kronos takes over his body, becoming the hero of the prophecy and ending the war on Percy's 16th birthday.