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:
Morganatic marriage
Perhaps the most famous example in modern times was the 1900 marriage of the heir to the throne of Austria-Hungary, Archduke Franz Ferdinand, and Bohemian aristocrat Countess Sophie Chotek von Chotkowa. The marriage was initially resisted by Emperor Franz Joseph I, but after pressure from family members and other European rulers, he relented in 1899 (but did not attend the wedding himself). The bride was made Princess (later Duchess) of Hohenberg, their children took their mother's new name and rank, but were excluded from the imperial succession. The Sarajevo assassination in 1914, killing both the Archduke Franz Ferdinand and his wife Sophie, triggered the First World War.