The succession, which was based on the principle of male primogeniture, was laid down in Lex Regia of 1665, which also regulated the royal house’s domestic relations in other ways. The democratic constitution of 5 June 1849 changed the monarchy’s status from absolute to constitutional. The Act of Succession of 27 March 1953 allowed for the possibility of female monarch; that is what enabled HM The Queen to accede to the throne in 1972.
In accordance with the Act of Succession of 1853, the throne passed to Frederik VII’s relative, Prince Christian of Glücksborg, who was a direct descendant of the Royal House. He acceded to the throne as Christian IX and became one of the longest reigning monarchs in Denmark (1863-1906). He was also the first monarch of the current House of Glücksborg. Christian IX eventually became known as the ¨father-in-law of Europe¨. His daughter, Princess Alexandra, married Edward VII of England.
Christian IX’s son, Frederik VIII, was 63 when he finally acceded to the throne in 1906. When he died in 1912, he was succeeded by his eldest son, Christian X, who reigned over Denmark throughout both World Wars. He is remembered as the "Equestrian King" because of his ride across the old border into the province of North Schleswig after its reunification with Denmark in 1920, and he became very popular during the German occupation of Denmark between 1940 and 1945 when, every day, he mounted his big white horse and rode through the streets of Copenhagen.