He married his cousin Hedwig Elizabeth Charlotte of Holstein-Gottorp (1759–1818), on 7 July 1774 in Stockholm. Both of their children died in infancy: 1. Lovisa Hedvig (Stockholm, 2 July 1797). Died at birth; buried at Riddarholmskyrkan (Riddarholm Church). 2. Carl Adolf, Duke of Värmland (Stockholm, 4 July 1798 – Stockholm, 10 July 1798). Lived six days; buried at Riddarholmskyrkan (Riddarholm Church). With Augusta von Fersen, he had an extramarital son: 1. Carl Löwenhielm 1772–1861 Adopted sons: 1. Charles August, Crown Prince of Sweden 2. Charles XIV John of Sweden