Question: What year did the father of Princess Ragnhild, Mrs. Lorentzen become King?

Context paragraphs:
Princess Astrid, Mrs. Ferner: Princess Astrid, Mrs. Ferner (Astrid Maud Ingeborg; born 12 February 1932 in Oslo, Norway) is the second daughter of King Olav V of Norway and his wife, Princess Märtha of Sweden.  She is the older sister of King Harald V of Norway and younger sister of the late Princess Ragnhild.

Riiser-Larsen Peninsula: Riiser-Larsen Peninsula (Norwegian: "Riiser-Larsenhalvøya" ) is a large peninsula forming the western portal to Lutzow-Holm Bay and marking the separation of the Princess Ragnhild and Prince Harald Coasts. Named for Captain Hjalmar Riiser-Larsen who discovered the peninsula in a flight from the "Norvegia" on February 21, 1931.

Erling Lorentzen: Erling Sven Lorentzen (born 28 January 1922) is a Norwegian shipowner and industrialist who has lived in Brazil for decades.  He founded Aracruz Celulose in 1968.  He is the widower of Princess Ragnhild.  He is a member of the Lorentzen family of shipping magnates.

Princess Ragnhild Coast: Princess Ragnhild Coast is the portion of the coast of Queen Maud Land in Antarctica lying between 20° E and the Riiser-Larsen Peninsula, at 34° E. All but the eastern end of the coast is fringed by ice shelves.  It was discovered by Capt. Hjalmar Riiser-Larsen and Capt. Nils Larsen in aerial flights from the ship Norvegia on February 16, 1931, and named for Princess Ragnhild of Norway.

Derwael Ice Rise: Derwael Ice Rise is 40 km long, 35 km wide and about 400 m tall ice rise in ice shelf off Princess Ragnhild Coast, Antarctica.  Situated 70 km east of Breid Bay in northern part of Roi Baudouin Ice Shelf, directly in front of Western Ragnhild Glacier.  Named for geodesist of Belgian Antarctic expedition Jean-Jacques Derwael.

Mount Gaston de Gerlache: Mount Gaston de Gerlache ( ) is the southernmost massif, 2,400 m high, in the Queen Fabiola Mountains of Antarctica.  It was discovered on 7 October 1960 by the Belgian Antarctic Expedition, 1960, under Guido Derom, and was named by Derom for Gaston de Gerlache, son of Adrien de Gerlache (leader of the first Belgian Antarctic Expedition, 1897–99).  Gaston led the Belgian Antarctic Expedition, 1957–58, which landed on Princess Ragnhild Coast and built the Roi Baudouin Station to carry out the scientific program of the International Geophysical Year.

Princess Ragnhild, Mrs. Lorentzen: Princess Ragnhild, Mrs. Lorentzen (Ragnhild Alexandra; 9 June 1930 – 16 September 2012) was the eldest child of King Olav V of Norway and Princess Märtha of Sweden.  She was the older sister of King Harald V and Princess Astrid.

Lorentzen family: Lorentzen or Bie-Lorentzen is a Norwegian family of Danish origin.  Several members have been noted as shipping magnates and industrialists.  Among its members are shipowner Erik Finn Lorentzen and industrialist Erling Lorentzen, who was married to Princess Ragnhild of Norway (known as Princess Ragnhild, Mrs. Lorentzen after her marriage), the eldest daughter of King Olav V of Norway.  Several members of the family are in the line of succession to the British throne; at the time of her death, Princess Ragnhild was number 75 and her children Haakon, Ingeborg and Ragnhild Lorentzen follow directly after.

Olav V of Norway: Olav V (born Prince Alexander of Denmark; 2 July 1903 – 17 January 1991) was King of Norway from 1957 until his death.

Johan Ferner: Johan Martin Ferner (né "Johan Martin Jacobsen"; 22 July 192724 January 2015) was a Norwegian sailor and Olympic medalist.  He won a silver medal in the 6 metre class with the boat "Elisabeth X" at the 1952 Summer Olympics in Helsinki, together with Finn Ferner (his brother), Erik Heiberg, Tor Arneberg and Carl Mortensen.  He was married to Princess Astrid, the sister of King Harald V of Norway.  He was also the brother-in-law of Princess Ragnhild.

Supporting paragraphs: Lorentzen family Olav V of Norway
Answer: 1957