Question: Prince Nicholas of Greece and Denmark was the son of which king that was assassinated in 1913?  

full_context: Document 1: Prince Nicholas of Romania: Prince Nicholas of Romania (Romanian: "Principele Nicolae a României" ; 5 August 1903 – 9 June 1978), later known as Prince Nicholas of Hohenzollern-Sigmaringen, was the fourth child and second son of King Ferdinand I of Romania and his wife Queen Marie.
Document 2: George William, Duke of Brunswick-Lüneburg: George William German: "Georg Wilhelm" (Herzberg am Harz, 26 January 1624 – 28 August 1705, Wienhausen) was Duke of Brunswick-Lüneburg. He ruled first over the Principality of Calenberg, a subdivision of the duchy, then over the Lüneburg subdivision. In 1689, he occupied the Duchy of Saxe-Lauenburg and passed it on to his successors. George William was the father of Sophia Dorothea of Celle, wife of George I of Great Britain.
Document 3: George I of Greece: George I (Greek: Γεώργιος Α΄ , "Geórgios I"; born Prince William of Schleswig-Holstein-Sonderburg-Glücksburg; 24 December 1845 – 18 March 1913) was King of Greece from 1863 until his assassination in 1913.
Document 4: Princess Elizabeth of Greece and Denmark: Princess Elisabeth of Greece and Denmark (Danish: "Elisabeth af Grækenland og Danmark" , Greek: Πριγκίπισσα Ελισάβετ της Ελλάδας και Δανίας or Ελισάβετ της Ελλάδας ; 24 May 1904 – 11 January 1955) was the middle daughter of Prince Nicholas of Greece and Grand Duchess Elena Vladimirovna of Russia.
Document 5: Prince William of Gloucester: Prince William of Gloucester (William Henry Andrew Frederick; 18 December 1941 – 28 August 1972) was a grandson of King George V of the United Kingdom and cousin of Queen Elizabeth II.
Document 6: Order of George I: The Royal Order of George I (Greek: Βασιλικόν Τάγμα Γεωργίου Α' ) is a Greek order instituted by King Constantine I in 1915. Since the monarchy's abolition in 1973, it is considered a dynastic order of the former Greek royal family.
Document 7: Prince Nikola of Yugoslavia (born 1958): Prince Nikolas of Yugoslavia (born 15 March 1958) is a member of the House of Karadordevic. Currently fourth in the line of succession to the defunct Yugoslavian throne, he is also in the line of succession to the British throne as a great-grandson of Princess Marie of Edinburgh, herself a granddaughter of Victoria of the United Kingdom.
Document 8: Prince George William of Great Britain: Prince George William of Great Britain (13 November 1717 – 17 February 1718) was an infant member of the British royal family, second son of George II and Caroline of Ansbach who, at the time of his birth, were the Prince and Princess of Wales. He died aged 3 months, 4 days.
Document 9: Grand Duchess Alexandra Georgievna of Russia: Grand Duchess Alexandra Georgievna of Russia (Russian: Алекса́ндра Гео́ргиевна ); "née" Princess Alexandra of Greece and Denmark (Greek: Πριγκίπισσα Αλεξάνδρα της Ελλάδας και της Δανίας ); 30 August 1870 – 24 September 1891) was the third child and firstborn daughter of King George I and Queen Olga of Greece, who herself was a daughter of a Russian grand duke, and was also a grandchild of Denmark's King Christian IX and Queen Louise. She was a sister to Constantine I of Greece, and thus aunt of three kings and two queens, Constantine's three sons, who all became kings of Greece, and two of his daughters, who were queens, in name, of Romania and Croatia, respectively. She was also first cousin of Tsar Nicholas II of Russia, King George V of the United Kingdom, and both King Haakon VII and Queen Maud of Norway, as well as a paternal aunt of Prince Philip, Duke of Edinburgh.
Document 10: William I of the Netherlands: William I (Willem Frederik, Prince of Orange-Nassau; 24 August 1772 – 12 December 1843) was a Prince of Orange and the first King of the Netherlands and Grand Duke of Luxembourg.
Document 11: Prince Nikolaos of Greece and Denmark: Prince Nikolaos of Greece and Denmark (born 1 October 1969) is the third child of Constantine II and Anne-Marie of Denmark, who were the last King and Queen of Greece, reigning from 1964 to 1973.
Document 12: Greek royal family: The Greek royal family (Greek: Ελληνική Βασιλική Οικογένεια) is a branch of the House of Glücksburg that reigned in Greece from 1863 to 1924 and again from 1935 to 1973. Its first monarch was George I, the second son of King Christian IX of Denmark. He and his successors styled themselves "Kings of the Hellenes". Most members of the dynasty (aside from the last king to reign, Constantine II and his queen consort, Anne-Marie of Denmark) hold the title "Prince or Princess of Greece and Denmark" with the style "Royal Highness", except Marina, Consort of Prince Michael, and their daughters Princess Alexandra and Princess Olga.
Document 13: Princess Tatiana of Greece and Denmark: Princess Tatiana of Greece and Denmark (born Tatiana Ellinka Blatnik, 28 August 1980) is the wife of Prince Nikolaos, son of Constantine II, who reigned as King of Greece until the monarchy was abolished in 1973.
Document 14: George I of Great Britain: George I (George Louis; German: "Georg Ludwig" ; 28 May 1660 – 11 June 1727) was King of Great Britain and Ireland from 1 August 1714 until his death, and ruler of the Duchy and Electorate of Brunswick-Lüneburg (Hanover) in the Holy Roman Empire from 1698.
Document 15: Prince Nicholas of Greece and Denmark: Prince Nicholas of Greece and Denmark (, 22 January 1872 – 8 February 1938), of the Glücksburg branch of the House of Oldenburg, was the fourth child and third son of King George I of Greece, and of Queen Olga. He was known as "Greek Nicky" in the family to distinguish him from his paternal first cousin Emperor Nicholas II of Russia. Prince Nicholas was a talented painter, often signing his works as "Nicolas Leprince."
ground_truth: George I