Task: Question Answering
Input (English): Passage: After further work as a répétiteur at the opera in Budapest, and with his standing enhanced by his association with Toscanini, Solti was given his first chance to conduct, on 11 March 1938. The opera was The Marriage of Figaro. During that evening, news came of the German invasion of Austria. Many Hungarians feared that Hitler would next invade Hungary; he did not do so, but Horthy, to strengthen his partnership with the Nazis, instituted anti-semitic laws, mirroring the Nuremberg Laws, restricting Hungary's Jews from engaging in professions. Solti's family urged him to move away. He went first to London, where he made his Covent Garden debut, conducting the London Philharmonic for a Russian ballet season. The reviewer in The Times was not impressed with Solti's efforts, finding them "too violent, for he lashed at the orchestra and flogged the music so that he endangered the delicate, evocative atmosphere." At about this time Solti dropped the name "György" in favour of "Georg".After his appearances in London Solti went to Switzerland to seek out Toscanini, who was conducting in Lucerne. Solti hoped that Toscanini would help find him a post in the US. He was unable to do so, but Solti found work and security in Switzerland as vocal coach to the tenor Max Hirzel, who was learning the role of Tristan in Wagner's opera. Throughout the Second World War, Solti remained in Switzerland. He did not see his father again: Mor Stern died of diabetes in a Budapest hospital in 1943. Solti was reunited with his mother and sister after the war. In Switzerland he could not obtain a work permit as a conductor, but earned his living as a piano teacher. After he won the 1942 Geneva International Piano Competition he was permitted to give piano recitals, but was still not allowed to conduct. During his exile, he met Hedwig (Hedi) Oeschli, daughter of a lecturer at Zürich University. They married in 1946. In his memoirs he wrote of her, "She was very elegant and sophisticated. ... Hedi gave me a little grace and taught me good manners – although she never completely succeeded in this. She also helped me enormously in my career". 
Question: What disease killed the father of the man who debuted with Covent Garden in London?
Output (English): diabetes.