Question: Who is the son of Princess Märtha of Sweden and King Olav V?
Context: European route E 10 is the second shortest Class A road which is part of the International E-road network.  It begins in Å, Norway and ends in Luleå, Sweden.  The road is about 850 km (530 mi) in length.  The Norwegian part of the road is also named Kong Olav Vs vei (King Olav V's road). Prince Olav of Norway (Norwegian: "Prins Olav" ) (1903-91), the future King Olav V held this title between 1905 and 1957. 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. 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. 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. Prince Olav Coast (Norwegian: "Kronprins Olav Kyst" ) is that portion of the coast of Queen Maud Land between the east entrance point of Lutzow-Holm Bay, marked by the coastal angle at 40° E, and Shinnan Glacier at 44° 38' E.  It was discovered by Capt. Hjalmar Riiser-Larsen in January 1930 on a flight from the Norvegia, and named for the future King Olav V of Norway. Princess Märtha of Sweden (Märtha Sofia Lovisa Dagmar Thyra; 28 March 1901 – 5 April 1954) was Crown Princess of Norway as the spouse of the future King Olav V from 1929 until her death in 1954.  The presently reigning King Harald V is her only son. Olavshallen (English: Olav Hall or Olav Concert Hall) was built in 1989 as a concert hall and is named after a historical tradition in Trondheim, Norway, the St. Olav tradition.  The foundation stone was laid by HRH King Olav V 22 July 1988.  Olavshallen opened for its first concert 17 September 1989 with jazz pianist Oscar Peterson and the official opening was held on 21 September. Olav V (born Prince Alexander of Denmark; 2 July 1903 – 17 January 1991) was King of Norway from 1957 until his death. Ormr inn Langi in Old Norse ("The Long Serpent") "Ormen Lange" in Norwegian, "Ormurin Langi" in Faroese was one of the most famous of the Viking longships.  It was built for the Norwegian King Olav Tryggvason, and was the largest and most powerful longship of its day.  In the late 990s King Olav was on a "Crusade" around the country to bring Christianity to Norway.  When he was traveling north to Hålogaland he came to a petty kingdom in today's Skjerstad, where the king named Raud the Strong refused to convert to Christianity.  A battle ensued, during which Saltstraum, a maelstrom that prevented reinforcements to the king's men, forced King Olav to flee.  He continued up north but returned some weeks later when the maelstrom had subsided.  Olav won the battle, captured Raud, and gave him two choices: die or convert.  The Sagas say that Olav tried to convert him but Raud cursed the name of Jesus, and the King became so enraged that he stuck a "kvanstilk" (a stalk of "Angelica", which are hollow) down his throat and shoved a snake into it, then a burning iron to force the snake down his throat.  The snake ate its way out of the side of the torso of Raud and killed him.  After the victory Olav confiscated Raud's riches, not least of which was Raud's ship, which he rechristened Ormen (The Serpent).  He took it to Trondheim and used it as a design for his own new ship, which he made a couple of "rooms" longer than Ormen and named Ormen Lange.
Answer: King Harald V