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:
Juan Carlos I of Spain
Juan Carlos was married in Athens on 14 May 1962, to Princess Sophia of Greece and Denmark, daughter of King Paul of Greece, first in a Roman Catholic ceremony at the Church of St. Denis, followed by a Greek Orthodox ceremony at the Metropolitan Cathedral of Athens. She converted from her Greek Orthodox religion to Roman Catholicism.