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:
Sophia (empress)
According to the "Ecclesiastic History" of John of Ephesus, Sophia was a niece of Theodora, the Empress consort of Justinian I. John of Ephesus did not specify the identities of her parents. According to the Secret History of Procopius, Theodora had only two siblings: her older sister Comito and younger sister Anastasia; either one could be the mother of Sophia. Procopius identifies Comito as a leading hetaera of her age. John Malalas records that Comito (b. ca 500) married general Sittas in 528. Sittas may thus be the father of Sophia. Whether Anastasia ever married is unknown.