3 Popes
“The king of France now abandoned the Avignon pope and declared himself neutral. The University of Paris did the same, and besought the two sets of cardinals to come together and work for reunion. Within a few weeks this had happened, and the majority of of the cardinals of both popes met in a common assembly. They summoned a council which met at Pisa …
“Both popes were cited to Pisa, and when they failed to appear were condemned in their absence for schism, heresy, and perjury, and deposed. Then the cardinals elected the archbishop of Milan … He took the name of Alexander V …
“The situation was now, in some respects, worse than ever. There were three popes instead of two, and in the end it was the third pope, the one of the threee who was most certainly not pope, whom practically the whole of Christendom obeyed …
“Pope Alexander lasted only ten months, and then the Pisan party elected to succeed him Baldassare Cossa, who took the name of John XXIII. He was a man so bad and so utterly unworthy of any ecclesiastical office–an ecclesiastical financier who had the name of having once been a pirate and was now a trader in indulgences–that in the end the emperor Sigismund intervened and set in motion the train of events which at last saved the Church.”
http://liturgicalnotes.blogspot.com/2023/10/illegitimate-popes-2.html