At the age of 15, real-life Lisa Gherardini married Florentine merchant Francesco del Giocondo â€“ who traded in female slaves shipped in from North Africa, authors say.
Mona Lisa posed with a dark smile because she was married off to a slave trader at just 15, a new book which investigated her family background suggests.
Lisa Gherardini, the real-life model who posed for Leonardo da Vinciâ€™s iconic painting, was pushed into a wedding with wealthy Florentine merchant Francesco del Giocondo.
He â€śregularly boughtâ€ť slave girls and shipped them over from North Africa before he converted them to Christianity, with many working as maids in the del Giocondo household in Florence.
But authors Martin Kemp and Giuseppe Pallanti, who researched Ms Gherardini in their book, Mona Lisa: The People and The Painting, believe del Giocondo transported more Moorish women than was needed for this work.
â€śThey could not have all remained in his household,â€ť the authors wrote. â€śThree were too many and one or all of them would have been sold on.â€ť
They suggest he was likely involved in trading the excess number of women he shipped into Florence before and after he married Ms Gherardini in 1495.
Her marriage to the wealthy merchant spawned a life of riches that was also chequered with scandal.
A story circulated that two men from the wealthy Medici family, of whom del Giocondo was a prominent supporter, made overtures to â€śtempt the honourâ€ť of Ms Gherardini â€“ but she rejected their advances.
Her husband feared for his business and standing in Florence and bolstered his support for the pair. They assured him their relationship sound â€“ but they secretly mocked him for his show of weakness.
Ms Gherardiniâ€™s sister Camilla, a nun, also stirred up another scandal when she and another sister were accused of allowing four men to touch them indecently, according to Mr Pallanti and Mr Kempâ€™s research.
The book states: â€śOn 20 April 1512, four men, armed and carrying a ladder, went to the convent of San Domenico, and having climbed the wall, reached certain small windows, where two nuns were waiting for them...they touched the breasts of said nuns and fondled other parts of their bodies, not to mention other indecencies.â€ť
It adds that two other nuns were supposedly â€śwatching with rapt attention, their eyes filled with similar desireâ€ť.
The case went to trial. The men involved were found guilty, but all four nuns were absolved.
After falling ill in her 60s, Ms Gherardini spent her later years in the same convent. She died in obscurity on 14 July 1542. The unfinished masterpiece, "Mona Lisa" - or Madame Lisa - did not turn her into an icon until centuries after she died.
As the years passed, word about the beauty of the painting spread. In 1857, the legendary novelist, poet and critic ThĂ©ophile Gautier sang its praises in an essay, stating: â€śYou discover that your melancholy arises from the fact that [Mona Lisa], three hundred years ago, greeted your avowal of love with the same mocking smile which she retains even today on her lips.â€ť
Her famous portrait, which is the most valuable painting in the world, hangs behind bullet-proof glass in the Louvre in Paris. Millions of visitors are lured from around the world to see the painting.
â€śEighty per cent of the people only want to see the Mona Lisa,â€ť former Louvre director Henri Loyrette told The New York Times. The painting is believed to be worth nearly $800m (ÂŁ620m).