Granted the title of "despotēs" by his father, the future Manuel II traveled west to seek support for the Byzantine Empire in 1365 and in 1370, serving as governor in Thessalonica from 1369. The failed attempt at usurpation by his older brother Andronikos IV Palaiologos in 1373 led to Manuel's being proclaimed heir and co-emperor of his father. In 1376–1379 and again in 1390 they were supplanted by Andronikos IV and then his son John VII, but Manuel personally defeated his nephew with help from the Republic of Venice in 1390. Although John V had been restored, Manuel was forced to go as an honorary hostage to the court of the Ottoman Sultan Bayezid I at Prousa (Bursa). During his stay, Manuel was forced to participate in the Ottoman campaign that reduced Philadelpheia, the last Byzantine enclave in Anatolia.