Complex sentence: Philippe d'Altoviti who's godfather was Philippe Emmanuel of Lorraine, Duke of Mercœur and brother of Queen Louise of Lorraine, was governor of Belle Ile for the king.
Split into simpler sentences: Philippe d'Altoviti who's godfather was Philippe Emmanuel of Lorraine, Duke of Mercœur (brother of Queen Louise of Lorraine). He was governor of Belle Ile for the king.