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:
Archduke Simeon of Austria
Simeon married Princess María of Bourbon-Two Sicilies, second-eldest daughter of Infante Carlos, Duke of Calabria and his wife Princess Anne of Orléans, on 13 July 1996 in La Toledana, Spain. Simeon is a (half) second cousin of his wife's father, both being great-grandchildren of Robert I, Duke of Parma. María's father descends from Duke Robert's first marriage and Simeon from the Duke's second marriage.