On June 26, 1409, Alexander V was elected as the newest pope by theologians and princes at the Council of Pisa. In the midst of the controversy involving the two popes in Avignon and Rome, the council had met to choose a new pope to replace both. The council’s objective backfired, however, as both reigning popes, Benedict XIII and Gregory XII, refused to acknowledge the newly elected pontiff. Similarly, Alexander V considered himself to be the rightful successor and declined to step down. The Catholic Church, then, had to deal with three popes – in Avignon, Rome, and Bologna – claiming legitimacy, until the Council of Constance (1414-1418) ended The Western Schism and instated Pope Martin V as the absolute papal authority in Rome.
Rosenwein, Barbara H. A Short History of the Middle Ages (4th ed.). (Toronto: University of Toronto Press Incorporated, 2014).
Images of Alexander V and Pope Gregory XII from Vaticinia de Summis Pontificibus (Munich, Bayerische Staatsbibliothek, Clm 313), 15th century.