Beelzebub, the gluttonous emperor of hell, master of calumny, foremost in wickedness and crime, is a fallen angel who presides over the Order of the Fly. Some say he is as high as a tower. Others say he has the figure of a snake, but with the generative organs of a young woman, and the face of a bluebottle.

Consequently, the god of Ekron’s first ever official visit to the Vatican last week was fraught with difficulties regarding imperial protocol, dietary requirements and appropriate toilet usage. To which facilities were the Swiss Guard to direct a pert-breasted snake-fly?

Pope Francis is a normally cheery man, but on seeing photos of his haunted visage on Wednesday, it seemed to me that a great sadness, a coal-black fear even, had seized his holy heart. At first I was confused. Had the pope, like me, read Morrissey’s comments on immigration and terrorism and realised that, after years of trying to make fanboy allowances for the singer’s pronouncements, he was finally going to have to throw away all his Smiths records?

Perhaps the pontiff had learned that Russell Howard was going to be replaced as host of Comedy Central’s Stand-Up Central by the less experienced Chris Ramsey, a source of anxiety not only to the pope, but to the brightly lit show’s hundreds of non-papal fans? Or was the leader of the world’s Catholics saddened by the death of Roger Moore, star of his favourite film, the 1980 marine insurance-themed thriller, North Sea Hijack?

(Though Moore was cast against type as the boorish misogynist marine insurance expert Rufus Excalibur ffolkes, Pope Francis is known to have admired the way Moore beatified the gruff, no-nonsense and decidedly politically incorrect character by making him a lover of cats. At the end of the movie, foul-mouthed ffolkes accepts only a litter of kittens as payment for thwarting Anthony “Psycho” Perkins’s perverted oil-rig hijack, snubbing grateful dignitaries to nurture the newborns with a saucer of milk.)

Sad-faced Pope Francis had my sympathy, whatever ailed him. I am not a religious or a superstitious person, despite having once been given a wedgie in a Paris mausoleum by the ghost of Napoleon, but like many atheists and agnostics I find in Francis much to admire, at least in comparison to all the evil popes that precede him.

Pope John XII raped pilgrims and drank toasts to a Satan; Pope Alexander VI had an incestuous relationship with his daughter and made naked boys leap from cakes; Pope Benedict XVI wore extravagant Prada shoes, sported a decadent red hat, and was a notoriously unenthusiastic member of the Hitler Youth, adding laziness as well as dressing as a young Nazi to his list of crimes.

But Pope Francis has never made naked things leap from cakes, worn prideful footwear, or drunk toasts to Satans, or indeed to any demons for that matter. Until now. And perhaps this explained the stunned horror that had spread across the usually illuminated fresco of his face on Wednesday.

Writing in his 1536 treatise Zodiacus Vitae, Marcellus Palingenius Stellatus described the monarch of hell as a menacing being of prodigious size, with a swollen chest, a bloated face, flashing eyes, large nostrils, and raised eyebrows, capable of changing his appearance into ever more terrifying aggregations of horror at will. And Pope Francis, it appeared, had broken with papal tradition to host Beelzebub and his entourage, for the first time ever, in Rome.

First, the Lie-father and his caravan of infernal harlots were given a tour of the Sistine Chapel, the Lord of Flies now choosing to manifest himself dressed like a bee, with two dreadful ears and his hair painted in all colours, with a dragon’s tail.

His retinue coiled around him in obedience, Beelzeboul stood before Michelangelo’s The Last Judgment, depicting souls weighed in the cosmic balance. But if Pope Francis had been intending to intimidate the White God into contrition by presenting him with the painting, he failed. Instead Ba’al, having asked if this Michelangelo guy was available for hotel lobby work, immediately took the form of a pile of dung, beset by flies, and slithered away.

The tour over, the historic summit between pope and Filth Lord began. As is customary, the two exchanged gifts. Francis gave Ba’al Zebûb a large medallion that depicted an olive, a symbol of peace. He also offered the Prince of Demons, who by now had become a goat-tailed calf with the face of a hornet, some of his latest writings (encyclicals), including his work on the need to protect the environment.

Belzebuth offered the pope a large box, filled with novelty condiment dispensers. Pope Francis’s advisers had warned him the Father of Lies might test him with an offering of unimaginable horror, which he was to accept unflinchingly, but Francis was taken by surprise. “This is a gift for you. The ketchup comes out of an asshole and the mustard is a shaved pussy,” the demon was overheard saying. “I think you will enjoy them. I hope you do.”

As the demon, now in the form of a bat with duck’s feet and a lion’s tail, moved towards the exit, he expressed gratitude to the man he once called disgraceful for questioning his beliefs. The dispute was related to Beel d’Bobo’s proposal to destroy all that is good and drag Christ down to Hades to subject him to eternal torment – a policy the pontiff had said was not Christian. The library door opened and the bat-faced duck-lion could be heard braying, “What’s done is done, Frankie. Now how about that mustard pussy?”

By the end of the half-hour private meeting, Pope Francis seemed forcedly jovial. He asked a wizened homunculus, swinging from the pendulous, bald testicles of the beast – who now appeared as a howling wolf with a lion’s head– what it gave its master to eat. It was unclear whether the being understood the remark, and it seemed to say, “pizza?” before smiling and answering, “yes”.

Pope Francis knows evil. He knows the contents of the demonic tracts chained in the Vatican’s secret library; he has read the suppressed internal reports his predecessors abandoned unresolved; and he has spent a lifetime fabricating plausible theological excuses for the cruelties of man and nature. But he has never had to confront, until now, corruption in a manifestation so blank and uncomprehending and unapologetic. In short, Francis’s visitor this week forced him to acknowledge evil in a different form, evil at its most banal. And his own impotence before it was written on his defeated papal face.