Just a legend or pure reality?. You decide.
According to medieval legend, Pope Joan was a female pope.
According to the legend, an English woman, educated in Mainz, dressed as a man and, due to the convincing nature of her disguise, became a monk before becoming a pope at a time when the method of selecting popes was haphazard. She took the name Pope John.
She was sexually promiscuous and became pregnant by one of her lovers. During an Easter Procession near the Basilica of San Clemente, over-enthusiastic crowds pushed around the horse which was carrying the 'Popess'. The horse reacted, almost causing an accident. The trauma of the experience led 'Pope John' to go into premature labour.
She was dragged feet-first by a horse through the streets of Rome, and stoned to death by the outraged crowd. She was buried in the street where her identity had been revealed, between the Lateran and St. Peter's Basilica. This street was (supposedly) avoided by subsequent papal processions - though when this latter detail became part of the popular legend in the 14th century, the Papacy was at Avignon, and there were no papal processions in Rome.
Supposedly, since that time, any candidate for the pope undergoes an intimate examination to ensure he is not a woman (or eunuch) in disguise. This involved sitting on a chair which has a hole in the seat. The most junior deacon present then feels under the chair to ensure the new Pope is male.
"And in order to demonstrate his worthiness, his testicles are felt by the junior present as testimony of his male sex. When this is found to be so, the person who feels them shouts out in a loud voice testiculos habet ("He has testicles") And all the clerics reply Deo Gratias ("Thanks be to God"). Then they proceed joyfully to the consecration of the pope-elect" - Felix Hamerlin, De nobilitate et Rusticate Dialogus (ca. 1490), quoted in The Female Pope, by Rosemary & Darroll Pardoe (1988).
https://www.fact-index.com/p/po/pope_joan.html
When I first saw this legend on the history channel, I thought it couldn't be true. However, around the same time that the legend is supposed to have ended with Pope Joan giving birth, the Popes procession route was changed to avoid the street that she was said to have been humiliated on. I can't remember the name, but it means cursed woman or something very close to that.
If you read the link provided in the original post, you would see this:
"The myth of Pope Joan was conclusively rubbished by David Blondel, a mid-seventeenth century protestant historian, who, through detailed analysis of the claims and suggested timings, showed that no such events could have happened. Among the evidence discrediting the Pope Joan story, is
* in the 'year of Pope Joan', 854, the actual pope was Leo IV.
* Papal possessions did not travel down the processional route where the supposed birth took place at Easter.
* No archival documentation exists of such an event.
* The 'testicle seat' which popes supposedly sat on to have their masculinity ascertained long predates the era of 'Pope Joan' and has nothing to do with a requirement that a pope have his tecticles checked."
There was no Pope John/Joan during the time-period... if you'd like, I can also point out the full lineage of Catholic Popes, dating back without time-breaks, to St. Peter himself:
https://catholicism.about.com/od/popes/a/cathpopes05.htm