Prussian regions, Royal Prussia, and the Polish crown's overlordship over the remaining Teutonic Monastic State, transformed in 1525 into a duchy, Ducal Prussia. Elisabeth's only brother Ladislaus, king of Bohemia and Hungary, died in 1457, and after that Casimir and Elisabeth's dynastic interests were directed also towards her brother's kingdoms. King Casimir IV died on 7 June 1492 in the Old Grodno Castle in the Grand Duchy of Lithuania, which was in a personal union with Poland. Foreign policies The intervention of the Roman curia, which hitherto had been hostile to Casimir, was due to the permutations of European politics. The pope was anxious to get rid of the Hussite King of Bohemia, George Podebrad, as the first step towards the formation of a league against the Ottoman Turks. Casimir was to be a leading factor in this combination, and he took advantage of it to procure the election of his son Vladislaus II as the King of Bohemia. But he would not commit himself too far, and his ulterior plans were frustrated by the rivalry of Matthias Corvinus, King of Hungary, who even went so far as to stimulate the Teutonic Order to rise against Casimir. The death of Matthias in 1490 was a great relief to Poland, and Casimir employed the two remaining years of his reign in consolidating his position still further. In 1490, Casimir's son John Albert was elected the King of Hungary by a party among the Hungarian nobles. He was, however, defeated by his older brother, King Vladislaus II of Bohemia. Casimir, who wanted to secure a separate realm for his sons, proposed John Albert. Most Hungarian barons and prelates preferred Vladislaus because his rule in Bohemia had indicated that he would respect their liberties. Vladislaus was crowned King of Hungary on 18 September 1490 in Székesfehérvár. Around 1480 Casimir was allied with the Great Horde against Muscovy and Crimea. His failure to support Khan Akhmed at the Great stand on the Ugra River contributed to Russia's gaining its independence from the steppe nomads. Tomb Casimir was interred at Wawel Cathedral in Kraków, in a red marble tomb sculpted by Veit Stoss. In 1973 a research team of 12 experts opened the tomb. Shortly afterward, 10 of the team died prematurely. It was subsequently found that the deaths were caused by toxins originating from fungus present in the tomb. Children Vladislaus (1 March 1456