Complex sentence: The ice broke and the king and his horse fell into the water, the king but not his horse was rescued by the horseman Thomas Larsson and Per Banér, who himself got into the water and was rescued by his younger brother Nils Banér.
Split into simpler sentences: The ice broke and the king and his horse fell into the water. The king (but not his horse) was rescued by the horsemen Thomas Larsson and Per Banér, who himself got into the water and was rescued by his younger brother Nils Banér.