15. John slept with his own niece and sisters
Taking a leaf out of his father’s (and possibly mother’s) book, John’s sexual appetites were so great he didn’t even stop at his own family. As Pope, remember, he could do whatever he wanted without getting into trouble (at least until God came calling, but he could worry about that later). Thus it was that John grew tired of having any woman he wanted, and decided to sleep with those who were forbidden to him by all conventional standards: his own niece and sisters. Their precise degree of relation to him is lost, not that there can be any mitigation.
But maybe there could be: this particular crime of incest was included in an extensive list of grievances against his misdemeanours compiled by John’s many enemies, and may have been exaggerated or the product of rumour and gossip. Repeating the sins of his own father has a biblical ring to it: ‘I the LORD thy God am a jealous God, visiting the iniquity of the fathers upon the children’ (Exodus 20:5). The charge, true or not, also provided a handy moral lesson for everyone about the foolishness of nepotism, which gave the church such a rubbish Pope.