A priceless portrait by the Venetian artist Titian has been rediscovered in the bowels of London's National Gallery.
The painting depicts Girolamo Fracastoro, the doctor who coined the name for the sexually transmitted disease syphilis in his 1530 poem.
An article in the gallery's Burlington Magazine by curators and scholars argues that evidence shows the painting must be by Titian, even though it had been attributed to a copycat for many years.
The painting was acquired by the National Gallery in 1924 after it was donated by Ludwig Mond. He had bought it as a Titian from Thomas Humphry Ward in 1895.
Prior to this, it had been owned by Charles Henfrey, an Englishman who bought the painting in 1854 while working as an engineer on the railway lines of northern Italy.
When he moved to Bengal in 1858, it is thought Henfrey was forced to sell his collection of paintings.
Cecil Gould discussed the portrait of Fracastoro in the Venetian School Cataloge and attributed it to a "Titian follower".
Art historian J P Richter believed it was by an artist called Torbido, rather than Titian, because Torbido was known to have painted Fracastoro.
Despite this lengthy history, experts have now come to agree that the painting is by Titian for a number of reasons. It is now known that Titian and Fracastoro knew one another, with the doctor sending his greetings to the artist in a 1539 letter.
Other evidence, such as an X-radiograph of the painting, show how the piece was composed: "Such approximate underdrawing does not support the suggestion that the National Gallery painting is a copy of a lost portrait. Furthermore the character of the lines is consistent with the underdrawing found in many of Titan's works."
The experts believe the portrait was painted in the late 1520s to the 1530s, around the time that Fracastoro published Syphilis (1530).
However, one problem encountered by the experts was how the portrait was in opposition to other likenesses of the artist: "Fracastoro's wary look is at odds with contemporary descriptions of his amiable, open and highly sociable nature. He looks ill at ease in what could have been his first experience of a portrait sitting.
"According to his biographer he did have very dark eyes, a think beard and a full head of black hair, but his face was round and his nose snub, the result of star gazing! This is puzzling for, during his lifetime, he was always represented with a sharp bony nose."
They add, however, that Titian often "flattered and regularised" his sitters features.
While the National Gallery says the painting is priceless, previous Titian paintings have sold for millions.
Titian's Sacra Conversazione: The Madonna and Child With Saints Luke and Catherine of Alexandria sold for £9.3 million in 2011, while the National Gallery secured the Diana and Callisto in a £45 million deal with the owner, the Duke of Sutherland.