Đurađ also maintained diplomatic relations with the Ottoman Empire. Đurađ owes his position and everlasting presence on the scene to his political cunningness. He succeeded the traditional rivalry between his family and Bosnian-Serbian King Tvrtko I Kotromanić, whose Serbian crown the Balšićs did not recognize, most probably because of their own claims to the Serbian throne1. On his diplomatic initiative, the Ottomans invaded Bosnia in 1386. During a second attack, Đurađ even sent his own troops to support the Ottoman Beylerbey of Rumelia Lala Şâhin Paşa at the Battle of Bileća on 27 August 1388, where he suffered a defeat to the hands of Bosnian Duke Vlatko Vuković Kosača. This led to the suspicion that Đurađ was an Ottoman vassal. The Ragusan Republic was weary of this Ottoman expansion, so they wanted to negotiate with Đurađ some military protection. On 23 August 1388 Đurađ sent his envoy Žanin Bareli, Filip's son.