Since the encounter at Pločnik in 1386, it was clear to Lazar that a decisive battle with the Ottomans was imminent. After he made peace with Sigismund, to avoid troubles on his northern borders, the prince secured military support from Vuk Branković and King Tvrtko. The King of the Serbs and Bosnia was also expecting a bigger Ottoman offensive since his army, commanded by Vlatko Vuković, wiped out a large Turkish raiding party in the Battle of Bileća in 1388. A massive Ottoman army led by Sultan Murad, estimated at between 27,000 and 30,000 men, advanced across the territory of Konstantin Dragaš and arrived in June 1389 on the Kosovo Field near Priština, on the territory of Vuk Branković. The Ottoman army was met by the forces commanded by Prince Lazar, estimated at between 12,000 and 30,000 men, which consisted of the prince's own troops, Vuk Branković's troops, and a contingent under the leadership of Vlatko Vuković sent by King Tvrtko. The Battle of Kosovo, the most famous battle in Serbia's medieval history, was fought on 15 June 1389. In the fierce fighting and mutual heavy losses, both Prince Lazar and Sultan Murad lost their lives.