Frederick IX (Danish: Christian Frederik Franz Michael Carl Valdemar Georg; 11 March 1899 – 14 January 1972) was King of Denmark from 1947 to 1972.[3] Born into the House of Glücksburg, Frederick was the elder son of King Christian X and Queen Alexandrine of Denmark. He became crown prince when his father succeeded as king in 1912. As a young man, he was educated at the Royal Danish Naval Academy. In 1935, he was married to Princess Ingrid of Sweden and they had three daughters, Margrethe, Benedikte and Anne-Marie. During Nazi Germany's occupation of Denmark, Frederick acted as regent on behalf of his father from 1942 until 1943.[4][5] Frederick became king on his father's death in early 1947. During Frederick IX's reign Danish society changed rapidly, the welfare state was expanded and, as a consequence of the booming economy of the 1960s, women entered the labour market. The modernization brought new demands on the monarchy and Frederick's role as a constitutional monarch. Frederick IX died in 1972, and was succeeded by his eldest daughter, Queen Margrethe II.