The Ottoman defeat at Ankara was used by John to negotiate a treaty with one of Bayezid I's sons, Süleyman Çelebi, in which the city of Thessalonica, as well as substantial territories in Thrace and Macedonia, were returned to the Byzantine Empire. John baptised and christianised two of Bayezid's sons in 1403: İsa Çelebi and Yusuf Çelebi. İsa may have been adopted by John, and Yusuf is recorded to have continued to live in Constantinople, attested there as late as 1413.
the OTTomAn dEfEat AT AnkAra waS USEd by JohN to negOTIATE a treaTy with One OF bAyezid i'S sOns, sülEyMaN çElebi, in whIch the cItY Of ThessalonICa, AS WELL as SubsTantiaL terRitories in thRace And MAcEdoniA, Were rEtUrnEd to the BYzaNtIne eMPire. jOhN bAPtiSeD And christianiseD Two OF baYezId's sOns IN 1403: İsA çelebi and yUsuf çelEbi. i̇sa may havE beeN adopted by JohN, and YUsuf is recoRDEd tO hAVE CONtInueD To live in constanTiNoPlE, atteStED tHerE as late aS 1413.