The Sultan showed his annoyance that the Byzantines had supported his uncle by putting them in prison; none of them were released until the conclusion of a treaty between John VIII and Murat in February 1424.
[1] He also played a heroic part in the final defense of Constantinople; according to Donald Nicol, he commanded a unit of 700 men stationed in the neighborhood of the Church of the Holy Apostles with his son-in-law Nikephoros Palaiologos, while Steven Runciman assigns him to a command of a portion of the Theodosian Walls next to the Sea of Marmora.
[4][5] Donald Nicol notes that a Demetrios Kantakouzenos is recorded as escaping from the fallen city, with his family and other refugees, on the ship of the Genoese admiral Zorzi Doria.
Doria took them as far as Chios, where the Venetian captain Thomas Celsi gave them passage to Candia (modern Heraklion) in Crete.
Nicol also mentions the record of the daughter of "one Demetrios Kantakouzenos and his wife Simonis Gadelina, called Maria" marrying Theodore, the son of Paul Palaiologos, in Corfu in November 1486.