Emperor John V Palaiologos had appealed to…

Emperor John V Palaiologos had appealed to the West for help after Ottoman Turks captured Edirne (Adrianopolis).

Instead, he had been detained in Venice as a debtor.

The regent Andronikos, his eldest son by his wife Helena Kantakouzene, whose maternal grandparents are John VI Kantakouzenos and Irene Asanina, had refused to pay the ransom for his father, and John had had to give up the island Tenedos (modern Bozcaada, Turkey) to buy his freedom.

After that event, John assigns his younger son Manuel as his crown prince and accepts the suzerainty of Ottomans in 1373.

Thus, when the Ottoman sultan asks for his services against some rebellions in Ottoman lands, he has to leave his capital.

This absence gives Andronikos a chance to rebel.

He allies with Murad's son Savcı Bey, who is rebelling against his own father, but both rebellions fail.

Murad I blinds and executes his son and demands that John V have Andronikos IV blinded as well, but John V blinds Andronikos in only one eye, imprisons him, and deprives him of his rights to the succession.