Question: What sovereign duke of the Duchy of Saxe-Coburg and Gotha, composed the opera Diana von Solange in 1858?
Context: Friedrich Josias, Prince of Saxe-Coburg and Gotha (Friedrich Josias Carl Eduard Ernst Kyrill Harald; Callenberg Castle, 29 November 1918 – Amstetten, Austria, 23 January 1998) was the head of the Ducal Family of Saxe-Coburg and Gotha and titular Duke of Saxe-Coburg and Gotha from 1954 until his death. Alfred (Alfred Ernest Albert; 6 August 184430 July 1900) reigned as Duke of Saxe-Coburg and Gotha from 1893 to 1900.  He was the second son and fourth child of Queen Victoria of the United Kingdom and Prince Albert of Saxe-Coburg and Gotha.  He was known as the Duke of Edinburgh from 1866 until he succeeded his paternal uncle Ernest II as the reigning Duke of Saxe-Coburg and Gotha in the German Empire. Diana von Solange is an opera by the German prince Ernst II of Saxe-Coburg-Gotha, an amateur composer.  It was premiered in 1858.  In 1859, Franz Liszt wrote an orchestral "Festmarsch nach Motiven von E. H. z. S-C-G", S.116, based on themes from "Diana von Solange" (E. H. z. S-C-G was short for Ernst Herzog zu Sachsen-Coburg-Gotha). Hubertus Prinz von Sachsen-Coburg und Gotha (Hubertus Alexis Richard Ernst Eduard; born 8 December 1961) is the eldest son of Ernst-Leopold Prinz von Sachsen-Coburg und Gotha ("aka" Prince Ernst Leopold of Saxe-Coburg and Gotha) and his first wife, Ingeborg Henig.  The Coburg branch of the Saxon dynasty, while ruling a small German duchy until 1918, provided constitutional kings to Belgium, Great Britain, Portugal and Bulgaria beginning in the 19th century, some of whose descendants continue to reign.  Hubertus is senior by descent in the male line of the post-1893 Coburgs, although it is the family's cadet branches which rose unexpectedly to international prominence and power in recent centuries, including giving queens consort to the German Empire, Norway, Romania and Italy. 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. Ernest I (German: "Ernst Anton Karl Ludwig Herzog" ; 2 January 1784 – 29 January 1844) was the last sovereign duke of Saxe-Coburg-Saalfeld (as Ernest III) and, from 1826, the first sovereign duke of Saxe-Coburg and Gotha (as Ernest I).  He was the father of Albert, Prince Consort of Queen Victoria and is thus a patrilineal ancestor and great-great-great-grandfather of Queen Elizabeth II.  Ernest fought against Napoleon Bonaparte and through construction projects and the establishment of a court theatre left a strong imprint on his residence town, Coburg. Princess Marie Luise Franziska "Amalie" of Saxe-Coburg and Gotha, full German name: "Marie Luise Franziska Amalie, Prinzessin von Sachsen-Coburg und Gotha, Herzogin zu Sachsen" (23 October 1848, Coburg, Saxe-Coburg and Gotha – 6 May 1894, Schloss Biederstein, Schwabing, Munich, Kingdom of Bavaria) was a Princess of Saxe-Coburg and Gotha by birth and a Duchess in Bavaria through her marriage to Duke Maximilian Emanuel in Bavaria.  Amalie was the fourth child and second eldest daughter of Prince August of Saxe-Coburg and Gotha and his wife Princess Clémentine of Orléans.  Her youngest brother was Ferdinand I of Bulgaria. In the redistribution of land among the Ernestine duchies that followed the death of the last Duke of Saxe-Gotha-Altenburg on 11 February 1825, the late Duke's nephew-in-law, Duke Ernst III of Saxe-Coburg-Saalfeld, received Gotha, while he ceded Saalfeld to the Duke of Saxe-Meiningen.  On 12 November 1826 he thus became Ernst I of Saxe-Coburg and Gotha.  The duchies of Saxe-Coburg and Saxe-Gotha remained in personal union until 1852, when a political union was effected. Ernest II (German: "Ernst August Karl Johann Leopold Alexander Eduard"; 21 June 1818 – 22 August 1893) was the sovereign duke of the Duchy of Saxe-Coburg and Gotha, reigning from 1844 to his death.  Ernest was born in Coburg as the eldest child of Ernest I, Duke of Saxe-Coburg-Saalfeld, and his duchess, Princess Louise of Saxe-Gotha-Altenburg.  Fourteen months later, his younger brother Prince Albert was born, who became consort of Queen Victoria of the United Kingdom.  Ernest's father became Duke of Saxe-Coburg and Gotha in 1826 through an exchange of territories. Andreas, Prince of Saxe-Coburg and Gotha, Duke of Saxony (given names: "Andreas Michael Friedrich Hans Armin Siegfried Hubertus"; born 21 March 1943) has been the head of the House of Saxe-Coburg and Gotha since 1998.  He is the grandson of Charles Edward, Duke of Saxe-Coburg and Gotha, the last ruling duke.
Answer: Ernest II