William IV (William Henry; 21 August 1765 – 20 June 1837) was King of the United Kingdom of Great Britain and Ireland and King of Hanover from 26 June 1830 until his death in 1837. The third son of George III, William succeeded his elder brother George IV, becoming the last king and penultimate monarch of the United Kingdom's House of Hanover. William served in the Royal Navy in his youth, spending time in British North America and the Caribbean, and was later nicknamed the "Sailor King". In 1789, he was created Duke of Clarence and St Andrews. Between 1791 and 1811, he cohabited with the actress Dorothea Jordan, with whom he had ten children. In 1818, he married Princess Adelaide of Saxe-Meiningen. He was appointed Britain's Lord High Admiral in 1827, the first since 1709. As his two elder brothers died without leaving legitimate issue, William inherited the throne when he was 64 years old. His reign saw several reforms: the Poor Law was updated, child labour restricted, slavery abolished in nearly all of the British Empire, and the electoral system refashioned by the Reform Act 1832. Although William did not engage in politics as much as his brother or his father, he was the last British monarch to appoint a prime minister contrary to the will of Parliament. He granted his German kingdom a short-lived liberal constitution. William had no surviving legitimate children at the time of his death, so he was succeeded by his niece Victoria in the United Kingdom and his brother Ernest Augustus in Hanover, ending the 123-year personal union between the two countries.