After the death of John VIII in 1448, Georgios entered the Pantokrator monastery in Constantinople under Constantine XI (1448–1453) and took, according to the invariable custom, a new name: Gennadius. Before the fall of the city he was already well known as a bitter opponent of the union. He and Mark of Ephesus were the leaders of the anti-Latin party. In 1444, Mark of Ephesus on his deathbed praised Gennadius's irreconcilable attitude towards the Latins and the union. It was to Gennadius that the angry people went after seeing the Uniate services in the great church of Hagia Sophia. It is said that he hid himself, but left a notice on the door of his cell: "O unhappy Romans, why have you forsaken the truth? Why do you not trust in God, instead of in the Italians? In losing your faith you will lose your city."