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 and Frederick William differed from each other in every aspect and the marriage suffered as a result. Sophia Dorothea was interested in art, science, literature and fashion, while Frederick William was described as an unpolished, uneducated and spartan military man with rough manners. Though he was never unfaithful to her, he was unable to win her affection. One of the most important differences between them was that Sophia Dorothea, unlike her husband, loved entertainment, something he regarded to be frivolous. Frederick William contemplated divorcing her the same year they married and, judging by her letters, accused her of not wanting to be married to him. According to Morgenstern, "He had none of that astonishing complaisance by which lovers, whether husbands or friends, seek to win the favor of the beloved object. As far as can be gathered from the words he occasionally let drop, the crossing of his first love might have been the innocent cause of this; and as the object of this passion, by the directions of her mother and grandmother, treated him with harshness, where, then, could he learn to make love?"