SYDNEY (AFP) - A mysterious Renaissance portrait has been identified as a painting by Dosso Dossi of legendary femme fatale Lucrezia Borgia, a major Australian art gallery said Tuesday. National Gallery of Victoria director Gerard Vaughan said the painting, entitled Portrait of a Youth by an unknown artist when it was acquired in London in 1965, could be the only surviving painted portrait of Lucrezia. "What was previously a portrait of an unknown sitter by an unidentified artist, now seems likely to be one of the most significant portraits surviving from the Renaissance, by one of the great Northern Italian painters", he said. Lucrezia Borgia was the illegitimate daughter of Cardinal Rodrigo Borgia, who ruled as Pope Alexander VI from 1492 to 1503 and whose family became known for corruption and scandal. The oval painting had baffled every expert on the subject since it came into public view during the twentieth century and had always been assumed to be of a young male, the gallery said in a statement. But years of detailed technical and art historical research by conservator Carl Villis has led to the conclusion that it is a work by Renaissance artist Dosso Dossi. "It has been very exciting to unlock the secrets of this beautiful and enigmatic painting, which now has unique standing in view of the fame of its sitter and the strength of the artist," said Villis. "Generations of art historians have attempted to identify portraits of Lucrezia Borgia, but this appears to be the only one which contains direct personal references to this intriguing historical figure. "The only reliable likeness of her features we have is on a portrait medal in bronze, made in 1502. The facial profile on the medal bears a striking resemblance to our portrait." The painting will go on public display identified as Dosso Dossi's Lucrezia Borgia from Wednesday.