The art world’s most famous face – Mona Lisa – may have belonged to a promiscuous courtesan who was nicknamed “the Tigress”, according to a decade of research by a leading art historian.

The true identity of the model for Leonardo da Vinci’s painting – produced between 1500 and 1506 – has puzzled art historians for years but now experts are convinced that new research presented by Leverkusen-based Magdalena Soest has lifted the lid on her shady past.

Ms Soest believes that Mona Lisa was in fact the Duchess of Forli and Imola, born Caterina Sforza, and has unearthed a contemporary picture painted in 1487 by Italian artist Lorenzo di Credi to prove it.

The German daily newspaper Bild Zeitung published a montage of the two portraits yesterday – revealing striking similarities. In the earlier picture the countess was 25 and not yet as famous as when Da Vinci later painted her around the age of 40. But the proud pose, the position of the arms and the enigmatic smile is clearly evident in both.

Ms Soest is also reported to have done detailed studies of the nose, hair, lips and cheek structure in order to arrive at her conclusion.

Caterina Sforza was born in 1462, the illegitimate daughter of Galeazzo Maria Sforza, the Duke of Milan, and the wife of one of his followers. She grew up to be a legendary beauty and was celebrated for her courage.

Together with her first husband Girolamo Riaria she led their troops in storming one of Rome’s greatest citadels, the Castel Sant’Angelo, in a bid to install their candidate as the Pope when Sixtus IV died in 1484.

In all, she married three times, had 11 children and countless lovers, but she was brought down in 1499 when she was imprisoned for a year by the Borgias for her plot to poison Pope Alexander VI. Her cities were seized by the infamous family and she retired to Florence, where she died in 1509, aged 46.

Art historians had previously believed that Da Vinci’s sitter was a young Florentine woman who married Francesco del Giocondo in 1495 and thus came to be known as La Gioconda. Other theories suggested she was a transvestite, a prostitute or even Da Vinci himself in drag.