Christian Albert's son Frederick IV (d. 1702) was again attacked by Denmark, but had a powerful champion in King Charles XII of Sweden, who secured his rights by the Treaty of Travendal in 1700. Frederick IV was killed at the Battle of Kliszów in 1702, and his brother Christian August acted as regent for his son Charles Frederick until 1718. In 1713 the regent broke the stipulated neutrality of the duchy in favour of Sweden and Frederick IV of Denmark seized the excuse to expel the duke by force of arms. Holstein was restored to him by the peace of Frederiksborg in 1720, but in the following year king Frederick IV was recognised as sole sovereign of Schleswig by the estates and by the partitioned-off dukes of the Augustenburg and Glücksburg lines.