Sofia Palaeologus

…of his ward and pupil, Zoë Palaeologus, niece of the last emperor of Byzantium. It took three years before Zoë, who, on entering Moscow, changed her name to Sofia (and perhaps her faith to Orthodoxy), was married to Ivan in the Kremlin.

…close to Ivan’s second wife, Sofia (Zoë) Palaeologus, opposed this; her son Vasily threatened and perhaps attempted an insurrection, and Ivan was forced to accept Vasily.