It is Florence in 1503. Leonardo da Vinci is beginning to paint his new commission, Lisa del Giocondo, the wife of Francesco del Giocondo, but he just can’t get the right expression. The story gives a clue to where the name of the painting actually came from.

It was early in the afternoon; Lisa had come to my studio in Florence for a preliminary sitting. I had agreed, much against my best opinion, to paint the wife of Francesco del Giocondo. Francesco was a silk merchant in Florence and had patronised me for many years, often furnishing silks for my models to wear. It was difficult for me to refuse his generosity, although I often wished I could. I think that I had always known that one day he would exact a price.

“Here, Leo,” he would say as we drank a lemon draught. “I have a bolt of beautiful green silk; use it with my pleasure for your next portrait.” He never asked for anything in return, and occasionally, he would bring his wife Lisa with him. He was a lucky man; Lisa was a rare beauty, a unique lady that I would have wished as my wife, but he took her at sixteen years old and has kept her mostly out of the public eye ever since.

I had set up my studio, ready for the sitting, with a couch and draped it with the bolt of green so generously given by Francesco. Behind was a window showing to the north, the streets of Florence winding away through it, but that mattered not; I could paint any background I chose, perhaps a winding path, perhaps a barren landscape. I had yet to decide.

Lisa arrived by carriage; she was accompanied by a servant of her husband to ensure her safe arrival. I told the man that Lisa would be with me for seven hours and that he should then return to take her back to her husband. The man nodded his agreement and then departed.

“How do you want me, Ser Vinci?” she asked me, her voice soft like velvet, assailing my senses, capturing my mind.

This would be our first sitting, and I was sure in my mind how I wanted her, but I wasn’t certain if I would achieve it today.

“Sit on the chaise, Lisa,” I said, "and turn towards me. I shall do a portrait of you, and I want you looking at me.”

Usually, portraits were done from the side, almost a silhouette, but I wanted to capture her essence. I wanted her eyes, I wanted the crease in her bosom; I wanted her to captivate the viewer, the viewer who I was sure would only ever be her husband.

She sat and turned to me, and my heart melted in that moment. I was desolate that del Giocondo had already claimed her; I was determined that I would do a portrait that no man would be able to walk away from without a feeling of need, of wanting.

I took my charcoal and began to sketch out my portrait, outlining her head and her shoulders, positioning her eyes, and defining the crease and flow that would be her bosom; all the time I wished she were without vestments, that I could see her true glory.

The day drew on, and I was beginning to get the portrait in my head. On my wooden board, it was just charcoal; I had yet to begin adding any colour, but that would take many months, perhaps years. I would add layer after layer of translucent paint to summon movement, emotion and intricate detail. This portrait would be my finest work; she deserved no less than my best.

After the man had returned and she had gone, and after I had cleaned myself, Mona Del Trattoria called to visit. She knew I often overfocused when I worked and got stuck in my head. I usually unwound with Cesare Borgia, but he had been called away, as Mona knew. Occasionally, Cesare would sit for me in my portraits, and only he, Mona, and I knew that he did.

I sometimes thought of the nine muses – daughters of Zeus and Mnemosyne. They were said to be the personifications of inspiration for the arts and humanities. Mona would have been one of the sisters, and in my heart, I would call upon her and ask for divine revelations to seep into my work. I would need all the power of the muses to perfect my portrait of Lisa.

“Oh, Leo, my love,” she said, her hands cupping my face, “you look troubled.”

“I am in three minds as to how to proceed with the portrait,” I said.

She looked at me, and her soft hand ran backwards across my cheek; a stirring disturbed my loins. Mona began to undo her vestments, and soon my eyes feasted upon her voluptuous breasts. Her nipples were large, but her areolas were small; it was as if she had stuck wine corks to her breasts. I revelled in her beauty. Her dress slipped down, revealing her centre. Her crease was thin; it was as if she didn’t have the lips many women did, simply a slit between one half of her being and the other.

I pulled off my smock, my cock standing proud, and I approached Mona. I wanted to taste her, to possess her, to have her, and to have her taste me. I was selfish; I wanted it all. Mona reached up and wrapped her fingers around my cock. She squeezed and she smiled; I gulped. Her other hand took my balls, pressing gently, yet enough to cause pain, and then she rolled my balls in her hand as if they were boules.

She leant forward, opened her mouth and inhaled my cock, her lips wrapping around it, her throat sucking, her tongue playing with my hole. My eyes closed, and I imagined it was Lisa del Giocondo and not Mona del Trattoria that was sucking my cock; my heart was doing Mona a disservice, but my cock overruled and pulsed in Mona’s hot and gloriously wet mouth.

I began to move; I was fucking her face, fucking the face of the girl who had come to relax my mind and better my capabilities at painting on the morrow. I restrained, I held back, I concentrated, and I tried to tense my balls. I did not want to seed her mouth; I wanted to fill her fanny, to flood her. I pulled back; my cock fell from her mouth with a soft plopping sound.

I fell to my knees and parted her legs; her slit, for that is all it was, opened and revealed her pink valley glistening with her desire. I leant forward, my nose just a few millimetres away from her centre, and I inhaled. I inhaled the intoxicating aroma of Mona Del Trattoria. My tongue snaked out, and its tip ran along her valley, tasting her wetness, my nose slipping along the canyon of her sex. Wanting more, needing more, I pressed my mouth against her, kissing, tasting, and sucking her valley; she gasped, pleasures flowing through her as surely as they flowed through me.

I found the hard little bump in her slit that gave her so much pleasure, and I nipped it with my teeth; she cried out. I tugged it, I licked it, and my fingers sought her opening, and I pushed inside her hotness. Inside, she was not smooth as you might think; there were bumps and ridges. My fingernails found them all, tracing her inner geography, each rise or fall eliciting a gasp of delight.

“Oh, sire," she gasped as my tongue conspired with my fingers and edged her towards completeness.

My cock demanded a role; it was not prepared to be a simple bystander. I reached up and pushed Mona’s shoulders, and she lay back flat on the couch. I rose, leaving her crotch glistening with wantonness, my nose dripping with her arousal, and I pushed her left leg off the couch, leaving her sex open for me, the pink of her valley contrasting the pale olive of her outer skin.

I climbed onto the couch, my knees between her leg and the couch edge, and I leant forward, my cock contacting her fanny, and I pressed hard; I was needy. Her desire was so strong that my cock slipped straight in with no pressure, and soon my belly pressed against hers, her wide-open eyes speaking of her pleasure. Her mouth parted and her teeth appeared, and she bit at her lips, below, her fanny contracting and pulsing about my cock.

I eased back, my cock leaving the heat of her tunnel and hovering at her entrance, her fanny fluttering, and then I pushed again, my foreskin rolling back as I plunged, my cock rim riding her bumps and ridges, scraping her fanny walls as I plumbed her depth. Her fingers dug into my back, her legs pulled up and wrapped around me, pushing as I pushed, relaxing as I eased back.

I increased my pace, my urgent needs driving my body, pushing in, my belly slapping against hers, her mouth letting forth grunts as I filled her fanny. The harder I fucked, the frustrations of my first sitting with Lisa del Giocondo faded away, the slaps that echoed around my studio increasing in frequency, my balls twitching and dancing between my legs.

I felt them tighten; I knew I was ready, and with a bellow I unleashed inside Mona del Trattoria. Spurt after spurt I filled and I flooded. Her fingers dug in cruelly, and her fanny clamped tight, squeezing every drop from my balls. Her back lifted, raising us both off the couch; she looked into my eyes, and she shrieked, the scream of the unholy, the call of the wanton

She bucked and twisted, her hands flapping on my back and her legs thrashing as her orgasm consumed her. Slowly she relaxed, her eyes opened and her face softened. I moved back, and my cock fell from her fanny. As I knelt back, I could see my white residue pouring from the blackness of her hole, and then, even as I watched, the blackness closed, and I was faced with just the pink glistening with my spunk.

I stood and stepped back; I was restored, my mind once more at peace, and my muse had banished my demons. As I moved back and stood, I looked across at Mona del Trattoria. Naked, she lay sideways on the couch that Lisa del Giocondo had posed on, her face resting on her hand. I saw her slit lying sideways, and realisation dawned, and I knew; her slit, still calling to me, consuming me, looked just like a thin smile, the smile I needed to put on Lisa del Giocondo, the enigmatic smile to complete her.

No one would ever know that the smile on Lisa’s face was actually Mona’s slit. My portrait would be of Lisa but also of Mona, and I would forever see the face of both the woman I had and the woman that I wanted: Mona and Lisa.