Charles August or Carl August was a Danish prince. He is best known for serving as Crown Prince of Sweden briefly in 1810, adopted by Charles XIII, before his sudden death from a stroke. Earlier, he had been a general in the Royal Danish Army as well as the Governor-general of Norway. His name before assuming the Swedish title in 1810 was Christian August of Schleswig-Holstein-Sonderburg-Augustenburg, or Christian August of Augustenburg for short.

Charles XIII, or Carl XIII, was King of Sweden from 1809 and King of Norway from 1814 to his death. He was the second son of King Adolf Frederick of Sweden and Louisa Ulrika of Prussia, sister of Frederick the Great.