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:
Paul-Philippe Hohenzollern
In 1918, the crown prince of Romania (the future King Carol II) married Zizi Lambrino. The wedding was annulled the following year because it contravened the royal house's statute—Lambrino was both a Romanian and a commoner, and the marriage took place without the consent of the king. The couple had one son, Carol Lambrino, the father of Paul Hohenzollern. In 1921, Crown Prince Carol married Princess Helen of Greece and Denmark, and they had a son who became King Michael I of Romania.