Yusuf Çelebi

Yusuf Çelebi (; 1392 – 1429) was an Ottoman prince and the son of Sultan Bayezid I who did not play an active role in the Ottoman Interregnum . In Byzantine sources and prosopographical records, his name and title are preserved as Tzalapès kyr Dēmētrios .

He arrived in Constantinople after 1402. According to Laonikos Chalkokondyles, he came of his own accord, independently of the princely hostages handed over to Emperor Manuel II Palaiologos by Süleyman Çelebi , probably to escape from the political crisis taking place during the civil war. Nevertheless, the Byzantine historian Doukas refers to his status as a hostage at the Byzantine court, where he was educated in a Byzantine school . During this period, he befriended the future emperor John VIII Palaiologos, with whom he became very close friends . He later converted to Christianity, taking the name "Dēmētrios" . He died of natural causes in 1429 .

Yusuf was betrothed to Theodora, daughter of Despot Theodore I Palaiologos of the Despotate of the Morea, marking the only recorded occurrence of a male Ottoman dynast being integrated into the Byzantine imperial family through marriage. His upbringing in Constantinople is also cited as a prominent example of an Ottoman prince receiving a Byzantine education while retaining his native Turkish language.