William I of Württemberg
On 24 January 1816, in Saint Petersburg, he married his first cousin, Grand Duchess Catherine Pavlovna of Russia (1788–1819), daughter of Emperor Paul I of Russia (1754–1801) and Princess Sophie Dorothea of Württemberg (1759–1828). The couple had two children:
Princess Sophie of Greece and Denmark
Although the youngest of four sisters, Sophie was the first to wed, marrying her second cousin-once-removed Prince Christoph of Hesse (1901–1943) on 15 December 1930 in Kronberg, Berlin; she was 16. A younger son of Prince Frederick Charles of Hesse and Princess Margaret of Prussia, Christoph was a great-grandson of Queen Victoria through her eldest daughter Victoria, Princess Royal, wife of Frederick III, German Emperor. A director in the Third Reich's Ministry of Air Forces and a commander in the German Air Reserves, Christoph held the rank of "Oberführer" in the Nazi "SS". On 7 October 1943, he was killed in an airplane accident in a war zone of the Apennine mountains near Forlì, Italy. His body was found two days later.