Charles August , Crown Prince of Sweden Charles August ( 9 July 1768 – 28 May 1810 ) 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 stroke . Earlier , he had been a general in the Royal Danish Army as well as the Danish Governor - general of Norway . His name before assuming the Swedish title in 1810 was Christian August of Schleswig - Holstein - Sonderburg - Augustenborg ; Christian August of Augustenborg for short . Family . He was born at in July 1768 as the son of Friedrich Christian I , Duke of Schleswig - Holstein - Sonderburg - Augustenburg ( 1721 – 1794 ) and Princess Charlotte of Schleswig - Holstein - Sonderburg - Plön ( 1744 – 1770 ) . He was a younger brother of Frederik Christian II , Duke of Augustenborg , brother - in - law of Princess Louise Auguste of Denmark and an uncle of Caroline Amalie of Augustenburg , Queen consort of Denmark and Christian August , Duke of Augustenborg . He did not marry . Career in Denmark and Norway . Christian August studied in Leipzig , and returned from there to Denmark in 1785 . He was appointed Lieutenant Colonel , and was promoted to Colonel in 1787 and Major General in 1790 . From 1797 he was stationed in Austria , joining the fight against Napoleon . He left Austria when the Treaty of Lunéville ended the War of the Second Coalition in 1801 . In 1803 Christian August was named commander of Fredriksten Fortress in Norway , assuming the position in 1804 . In 1807 he once again became involved in the Napoleonic Wars , this time on the side of Napoleon as Napoleon ' s enemy Great Britain assaulted Denmark . The Danish - Norwegian part of the Napoleonic Wars is called the Gunboat War . Sweden joined forces against Denmark - Norway in 1808 . Christian August was a central figure in the war , and led forces to victories in the Battle of Prestebakke and the Battle of Toverud , ousting Swedish forces from Norway . In 1808 Christian August was promoted to Field Marshal , and in 1809 he became Governor - general of Norway . Sweden . On 6 June 1809 the Duke - regent of Sweden was proclaimed King , after Gustav IV Adolf was deposed . The new king Charles XIII accepted the new , liberal Constitution , which was ratified by the Riksdag of the Estates the same day . The new king was in no way likely to interfere with the liberal revolution which had placed him on the throne . Peace was what the exhausted nation now required . Charles XIII was childless , so in order to secure the succession to the throne , someone had to be he adopted as his heir . Georg Adlersparre , the main orchestrator of the 1809 coup , preferred Frederick VI of Denmark as the new Swedish monarch , but when Frederick refused , Adlersparre looked to Norway . He tried to persuade Christian August , first through the Swedish Baron C . H . Anckarsvärd , and although Christian August did not show up to meet Anckarsvärd personally , he gradually accepted the offer of adoption . His loyalty to his ruler Frederick VI ultimately became a lesser obstacle . The choice of Christian August was supported by Charles XIII as well as three of the estates of the realm ; the Clergy , Burghers and Peasants . However , the Nobility was more reluctant due to the influence of so - called ( " Gustavianerna " ) , supporting the deposed King Gustav IV Adolf and his then - underage son . The decision to adopt Charles August became definitive on 15 July 1809 . His great popularity in Norway was considered an advantage to the Swedish plans for the acquisition of that country . In addition , he had demonstrated his interest in a rapprochement between the two countries by refraining from invading Sweden during the Finnish War with Russia . After the Treaty of Fredrikshamn between Sweden and Russia on 17 September 1809 which concluded the Finnish War , Sweden was ready for the inauguration of Charles August . He finally left Norway for Sweden on 7 January 1810 . As Crown Prince of Sweden , he changed his name to Charles August ( ) . Honors were lavished upon him on his arrival , he was for example made an honorary member of the Royal Swedish Academy of Sciences on April 18 , 1810 , and was the first person to enjoy this status in that academy . However , he did not live long enough to make a historical impact in Sweden . He suddenly died on 28 May 1810 , when he fell off his horse during a military practice in Kvidinge . His autopsy confirmed that he had died of a stroke , but at the same time rumours went that he had been poisoned by Gustavians . Specifically , the Marshal Count Axel von Fersen was openly accused of having killed Charles August , and was lynched on 20 June 1810 during the funeral procession of Charles August . Charles August was buried in Riddarholmen Church , the burial church of Swedish monarchs . Legacy and aftermath . A monument to Charles August was commissioned by Prince Frederik of Hesse and erected in 1810 in the royal park at Bygdøy near Oslo . Before his departure from Oslo , a grand farewell party was held in his honour , and a group of wealthy citizens formed the charitable foundation . It acquired a large town house which still bears his name . A street in Oslo , , was named after him in 1852 . Charles August ' s successor as adopted Crown Prince , who was accepted by the Riksdag of the Estates in August , was Jean - Baptiste Bernadotte . External links .