Complex sentence: The voice that Lloyd heard in his room was none other than Kratos Aurion; a supposed mercenary who had first joined the group only to later betray them, revealing that he was a member of Cruxis, the antagonist organisation in the game.
Split into simpler sentences: The voice that Lloyd heard in his room was none other than Kratos Aurion; a supposed mercenary who had first joined the group. Then he had betrayed them, revealing that he was a member of Cruxis, the antagonist organisation in the game.