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:
Sophie Marie of Hesse-Darmstadt
On 9 February 1681 in Darmstadt, she married Duke Christian of Saxe-Eisenberg. At the time, he was a widower and father of a daughter. He had become the first Duke of Saxe-Eisenberg when Saxe-Gotha had been divided by Christian and his six brothers the year before. They had no children and Christian died without leaving an heir. A dispute erupted among the remaining brothers and their descendants about he inheritance of Saxe-Eisenberg.