After the defeat of the Serbs and Bosniaks in the Battle of Kosovo on 15 June 1389, Ivan Shishman had to seek help from Hungary. During the winter of 1391–1392, he entered into secret negotiations with the King of Hungary Sigismund, who was planning a campaign against the Turks. The new Ottoman sultan Bayezid I pretended to have peaceful intentions in order to cut off Ivan Shishman from his alliance with the Hungarians. However, in the spring of 1393 Bayezid gathered a large army from his dominions in the Balkans and Asia Minor and attacked Bulgaria. The Ottomans marched to the capital Tarnovo and besieged it. The defence of the capital was led by Patriarch Evtimiy because Ivan Shishman was located in Nikopol, presumably for better communication with Sigismund. After a three-month siege, Tarnovo fell on 17 July. According to the contemporary Bulgarian scholar and cleric Gregory Tsamblak, the city was not captured because of the Ottoman military strength but due to treason. The Ottoman campaign of 1393 devastated Bulgaria; in the wake of that invasion, the lands of Ivan Shishman were limited to Nikopol and several towns along the Danube. Upon his return from Wallachia after the Battle of Rovine in 1395, Bayezid I attacked and captured Nikopol and, according to the "Anonymous Bulgarian Chronicle", murdered Ivan Shishman on 3 June 1395. A Byzantine chronicle gives the date as 29 October. However, some sources suggest that the Bulgarian ruler was captured and died in prison.