Question: Who is Frederick Ix Of Denmark's father-in-law?

Knowledge 1: Frederick IX of Denmark
Frederick IX (Christian Frederik Franz Michael Carl Valdemar Georg; 11 March 1899 – 14 January 1972) was King of Denmark from 1947 to 1972.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.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. [SEP] Knowledge 2: Ingrid of Sweden
Ingrid of Sweden(Ingrid Victoria Sofia Louise Margareta; 28 March 1910 – 7 November 2000) was Queen of Denmark from 1947 until 1972 as the wife of King Frederick IX.Born into the House of Bernadotte, she was the daughter of King Gustaf VI Adolf of Sweden and his first wife, Princess Margaret of Connaught.In 1935 she married Crown Prince Frederick of Denmark and they had three daughters, Margrethe, the present Queen of Denmark, Benedikte, now a Princess of Sayn-Wittgenstein-Berleburg, and Anne-Marie, the former Greek queen.In 1947, her husband became king on his father's death.As queen, Ingrid reformed the traditions of Danish court life, abolished many old-fashioned customs at court and created a more relaxed atmosphere at official receptions.King Frederick IX died in 1972, and Ingrid's daughter Margrethe became queen.She was also a paternal aunt of the present Swedish monarch, King Carl XVI Gustaf.
Knowledge 1: Frederick IX of Denmark
Frederick IX (Christian Frederik Franz Michael Carl Valdemar Georg; 11 March 1899 – 14 January 1972) was King of Denmark from 1947 to 1972.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.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. [SEP] Knowledge 2: Louise of Hesse-Kassel
Louise of Hesse-Kassel (7 September 1817 – 29 September 1898) was Queen of Denmark by marriage to King Christian IX of Denmark.
Knowledge 1: Ingrid of Sweden
Ingrid of Sweden(Ingrid Victoria Sofia Louise Margareta; 28 March 1910 – 7 November 2000) was Queen of Denmark from 1947 until 1972 as the wife of King Frederick IX.Born into the House of Bernadotte, she was the daughter of King Gustaf VI Adolf of Sweden and his first wife, Princess Margaret of Connaught.In 1935 she married Crown Prince Frederick of Denmark and they had three daughters, Margrethe, the present Queen of Denmark, Benedikte, now a Princess of Sayn-Wittgenstein-Berleburg, and Anne-Marie, the former Greek queen.In 1947, her husband became king on his father's death.As queen, Ingrid reformed the traditions of Danish court life, abolished many old-fashioned customs at court and created a more relaxed atmosphere at official receptions.King Frederick IX died in 1972, and Ingrid's daughter Margrethe became queen.She was also a paternal aunt of the present Swedish monarch, King Carl XVI Gustaf. [SEP] Knowledge 2: Louise of Hesse-Kassel
Louise of Hesse-Kassel (7 September 1817 – 29 September 1898) was Queen of Denmark by marriage to King Christian IX of Denmark.

Answer: Gustaf VI Adolf of Sweden