Fazıl Mustafa Pasha's victory at Belgrade was a major military achievement that gave the Ottomans hope that the military debacles of the 1680s—which had led to the loss of Hungary and Transylvania, an Ottoman vassal principality ruled by pro-Istanbul Hungarian princes— could be reversed. However, the Ottoman success proved ephemeral. On 19 August 1691, Fazıl Mustafa Pasha suffered a devastating defeat at the Battle of Slankamen at the hands of Ludwig Wilhelm von Baden, the Habsburg commander in chief in Hungary, nicknamed “Türkenlouis” (Louis the Turk) for his victories against the Ottomans. In the confrontation, recognized by contemporaries as “the bloodiest battle of the century,” the Ottomans suffered heavy losses: 20,000 men, including the grand vizier. With him, the sultan lost his most capable military commander and the last member of the Köprülü family, who for the previous half century had been instrumental in strengthening the Ottoman military.