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 of Württemberg
She was born in Stuttgart; her parents were King William I of Württemberg and Grand Duchess Catherine Pavlovna of Russia, the fourth eldest daughter of Tsar Paul I. Sophie and William were first cousins as their mothers were sisters. Shortly after Sophie’s birth, her mother died, and she was cared for by her aunt, Catharina of Württemberg. She was niece of tsars Alexander I and Nicholas I of Russia and a cousin of Tsar Alexander II, George V of Hanover and England's Queen Victoria.