Complex sentence: She had purportedly desired to marry her cousin William of Orange, who would later become King of England, though her family believed that sacrifices needed to be made in order to make a more beneficial marriage with the recently widowed brother of the King of France.
Split into simpler sentences: She had purportedly desired to marry her cousin William of Orange, who would later become King of England. Though her family believed that sacrifices needed to be made in order to make a more beneficial marriage with the recently widowed brother of the King of France.