Question: From when was the father of Ernst Gunther pretender to the throne of Schleswig-Holstein?

Context paragraphs:
Klonimir: Klonimir (, ; fl.  896) was a Serbian prince of the Vlastimirović dynasty, and pretender to the throne of the Serbian Principality.  His father and uncle, co-princes Strojimir and Gojnik, had been exiled to Bulgaria with their families after their eldest brother Mutimir had ousted them and taken the Serbian throne.  Klonimir married a Bulgarian noblewoman chosen by Khan Boris I himself.  She later gave birth to a son named Časlav.  The descendants of the three Vlastimirović branches continued the feud over the Serbian throne which spanned over the century, and Klonimir returned to Serbia in ca. 896 and attempted to take the country from his cousin Petar, who had ruled since 891.  He managed to take over the Serbian city of Destinikon, but the much more powerful Petar defeated him, and it is presumed that Klonimir died in battle.  His son Časlav later became the most powerful of the Vlastimirović dynasty, as Prince of Serbia from 927 to 960, unifying several tribes in the region.

Charles Edward Stuart: Charles Edward Louis John Casimir Sylvester Severino Maria Stuart (31 December 1720 – 31 January 1788), commonly known in Britain during his lifetime as The Young Pretender and The Young Chevalier, and often known in retrospective accounts as Bonnie Prince Charlie, was the second Jacobite pretender to the thrones of England, Scotland, France and Ireland (as Charles III) from the death of his father in 1766.  This claim was based on his status as the eldest son of James Francis Edward Stuart, himself the son of James VII and II.  Charles is perhaps best known as the instigator of the unsuccessful Jacobite uprising of 1745, in which he led an insurrection to restore his family to the throne of Great Britain.  The uprising ended in defeat at the Battle of Culloden, effectively terminating the Jacobite cause.  Jacobites supported the Stuart claim because they hoped for religious toleration for Roman Catholics and because they believed in the divine right of kings.  Charles's flight from Scotland after the uprising has rendered him a romantic figure of heroic failure in some later representations.  In 1759 he was involved in a French plan to invade Britain, which was abandoned after British naval victories.

Frederick VIII, Duke of Schleswig-Holstein: Duke Frederick VIII (Danish: "Frederik Christian August af Slesvig-Holsten-Sønderborg-Augustenborg" ; German: "Friedrich Herzog von Schleswig-Holstein-Sonderburg-Augustenburg" ) (July 6, 1829 – January 14, 1880) was the German pretender to the throne of Schleswig-Holstein from 1863, although in reality Prussia took overlordship and real administrative power.

Ernst Gunther, Duke of Schleswig-Holstein: Ernst Gunther, Duke of Schleswig-Holstein (August 11, 1863 – February 22, 1921) was a son of Frederick VIII, Duke of Schleswig-Holstein and Princess Adelheid of Hohenlohe-Langenburg.  He inherited his father's title as titular duke of Schleswig-Holstein.

Line of succession to the former throne of Anhalt: The Duchy of Anhalt was abolished in 1918 during the German Revolution, following the defeat of the Central Powers in the First World War.  The original succession principle was semi-salic, with the nearest female kinswoman of the last male inheriting the crown upon extinction of the dynasty in the male line.  The current pretender to the throne and head of the house is Eduard, Prince of Anhalt, son of Joachim Ernst, the last ruling Duke of Anhalt.

Correspondence with the Pretender Act 1697: The Correspondence with the Pretender Act 1697 (9 Will.3 c. 1) was an Act of the Parliament of England which made it high treason to correspond with the deposed King James II.  (This Act replaced an earlier Act of 1691.)  When James II died and his son "James III" asserted his own claim to the throne, the Correspondence with James the Pretender (High Treason) Act 1701 was passed to replace this provision.

Michael, Prince of Montenegro: Prince Michael Petrović-Njegoš of Montenegro (14 September 1908 – 24 March 1986) was the third (but eldest surviving) son of Prince Mirko of Montenegro, Grand Voivode of Grahovo and Zeta (1879–1918), and Natalija Konstantinovic, a cousin of Aleksandar Obrenović of Serbia.  He was pretender to the throne of Montenegro, holding the title Grand Duke of Grahovo and Zeta, in succession to his father.  Nicholas I of Montenegro was Michael's grandfather.  Michael had recognized and acknowledged the Unification of Montenegro with Serbia, renouncing the throne.  In World War II he was held prisoner by the Nazis after refusing to take up the throne of the Axis forces' re-established Montenegrin puppet-state.  During the period of Communism, he was an active member of the Serb diaspora revolutionary organization and a diplomatic worker against the Communist dictatorship of Marshal Tito.

Princess Dorothea of Saxe-Coburg and Gotha: Princess Dorothea Maria Henriette Auguste Louise of Saxe-Coburg and Gotha (30 April 1881 – 21 January 1967) was a princess of Saxe-Coburg and Gotha (German: "Prinzessin von Sachsen-Coburg und Gotha" ) by birth and the duchess of Schleswig-Holstein (German: "Herzogin zu Sachsen" ) through her marriage to Ernst Gunther, duke of Schleswig-Holstein.  Dorothea was born in Vienna, Austria, the second child and only daughter of Prince Philipp of Saxe-Coburg and Gotha and Princess Louise of Belgium.

Peter, Duke of Schleswig-Holstein: Peter, Duke of Schleswig-Holstein (German: "Friedrich Ernst Peter" ; 30 April 1922 in Schloss Louisenlund, Schleswig, Schleswig-Holstein, Germany – 30 September 1980 in Bienebek, Schleswig-Holstein, West Germany) was the Duke of Schleswig-Holstein and Head of both the House of Glücksburg and the entire House of Oldenburg from 10 February 1965 until his death on 30 September 1980.  Peter was the third and youngest son of Wilhelm Friedrich, Duke of Schleswig-Holstein and his wife, Princess Marie Melita of Hohenlohe-Langenburg.  He was a great-great-grandson of Queen Victoria through her second son, Prince Alfred.

Prince Xavier of Bourbon-Parma: Xavier, Duke of Parma and Piacenza, in France known before 1974 as Prince Xavier de Bourbon-Parme, in Spain known as Francisco Javier de Borbón-Parma y de Braganza or simply as Don Javier (25 May 1889 – 7 May 1977) was the head of the ducal House of Bourbon-Parma.  He is best known as dynastic leader of Carlism and the Carlist pretender to the throne of Spain, since 1936 as a regent-claimant and since 1952 as a claimant, appearing under the name Javier I.  Since 1974 he was pretender to the defunct throne of Parma.  He is also recognized as involved in the so-called Sixtus Affair of 1916-1917 and the so-called Halifax-Chevalier talks of 1940.

Supporting paragraphs: Ernst Gunther, Duke of Schleswig-Holstein Frederick VIII, Duke of Schleswig-Holstein
Answer: 1863