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:
Queen Sofía of Spain
The couple married on 14 May 1962, at the Catholic Cathedral of Saint Dionysius in Athens. The bride's gown was made by Jean Dessès and she was attended by her sister Princess Irene of Greece and Denmark, the groom's sister Infanta Pilar of Spain, and Sofía's future sister-in-law Princess Anne-Marie of Denmark (later Queen of Greece), along with Princess Irene of the Netherlands, Princess Alexandra of Kent, Princess Benedikte of Denmark, Princess Anne of Orléans and Princess Tatiana Radziwill.