Lucrezia was the daughter of Rodrigo Borgia, later Pope Alexander VI
A mysterious Renaissance portrait has been identified as a painting of infamous Italian femme fatale Lucrezia Borgia by artist Dosso Dossi.
Australia's National Gallery of Victoria said it could be the only surviving painted portrait of Lucrezia.
It was entitled Portrait of a Youth by an unknown artist when it was acquired in London in 1965.
Gallery director Gerard Vaughan said it now seemed to be a "significant" portrait from the Renaissance period.
The painting will go on public display identified as Dossi's Lucrezia Borgia later this week, following years of painstaking research, the gallery said.
"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", said Mr Vaughan.
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 20th century and had always been assumed to be of a young man, the gallery said in a statement.
But following research by conservator Carl Villis, it is now believed to be the work of Dossi from the early 16th century.
"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 Mr 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."