Complex sentence: After a long and dangerous journey, she freed the old Guardian and brought him to his Realm, where they discovered that the next Guardian is not herself but Vanguard's second-in-command, Gordon Halloway, who had been pursuing her throughout the game.
Split into simpler sentences: After a long and dangerous journey, she freed the old Guardian and brought him to his Realm. But once there, they discovered that the next Guardian is, after all, not her but Vanguard's second-in-command, Gordon Halloway, who had been pursuing her throughout the game.