Frederick became King of Denmark-Norway on 13 March 1808. When the throne of Sweden seemed likely to become vacant in 1809, Frederick was interested in being elected there as well. Frederick actually was the first monarch of Denmark and Norway to descend from Gustav I of Sweden, who had secured Sweden's independence in 1520s after the period of the Kalmar Union with other Scandinavian countries. However, Frederick's brother-in-law, Prince Christian Augustus of Augustenborg, was first elected to the throne of Sweden, followed by the French Marshal Bernadotte.