Unrecognised Leonardo da Vinci portrait revealed by his fingerprint

According to Timesonline, the portrait known as Young Girl in Profile in Renaissance Dress, or La Bella Principessa, is a work by Leonardo da Vinci. A fingerprint in the top left corner appears to have confirmed this extraordinary art discoveries. Martin Kemp, Emeritus Professor of History of Art at the University of Oxford, is convinced the woman should be Bianca Sforza, daughter of Ludovico Sforza, Duke of Milan (1452-1508), and his mistress Bernardina de Corradis.