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English: Cardinal Isidore of Kiev, also known as Isidore of Thessalonica (Greek: Ἰσίδωρος τοῦ Κιέβου; Russian: Исидор; Ukrainian: Ісидор; 1385 – 27 April 1463), was a prelate of Byzantine Greek origin. From 1437 to 1441 he served as the Metropolitan of Kiev and all Rus' in the patriarchate of Constantinople of the Eastern Orthodox Church. He was a supporter of the Union of Florence which he proclaimed in Hagia Sophia on 12 December 1452. In the Latin Church, Isidore was the cardinal bishop of Sabina, Archbishop of Cyprus, Camerlengo of the Sacred College of Cardinals and the Latin Patriarch of Constantinople.