Answer
Patriarch John of Antioch was excluded from the Council of Ephesus by Cyril due to a dispute over the condemnation of Nestorius. Cyril accused Nestorius of heresy for distinguishing between the divine and human natures of Christ, while John supported Nestorius's position. The conflict escalated, and Cyril, with the support of the emperor, secured John's exclusion from the council, further deepening the divisions within the early Christian Church.