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 Dorothea of Hanover
Sophia Dorothea married her cousin, Crown Prince Frederick William of Prussia, heir apparent to the Prussian throne, on 28 November 1706. They had met as children when Frederick William had spent some time in Hanover under the care of their grandmother, Sophia of Hanover, and though Sophia Dorothea disliked him, Frederick William had reportedly felt an attraction to her early on.