He is the youngest child and only son of Prince Gustaf Adolf , Duke of Västerbotten , and Princess Sibylla of Saxe-Coburg and Gotha . His father died on 26 January 1947 in an airplane crash in Denmark when Carl Gustaf was nine months old . Upon his father 's death , he became second in line to the throne , after his grandfather , the then Crown Prince Gustaf Adolf . Following the death of his great-grandfather King Gustaf V in 1950 , Gustaf Adolf ascended the throne and thus Carl Gustaf became Sweden 's new crown prince and heir apparent to the throne at the age of four
in an airplane crash
1947 KLM Douglas DC-3 Copenhagen accident
Carl XVI Gustaf of Sweden