Frederick I (Christian Frederik Franz Michael Carl Valdemar Georg; 11 March 1899 – 14 January 1972) was King of Denmark from 1947 to 1951 and King of Kalmar Union from 1951 to 1972. Born into the House of Glücksburg, Frederick was the eldest son of King Christian X of Denmark 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.