Lucrezia Borgia, Duchess of Ferrara, by Dosso Dossi, c 1518. The painting was originally thought to be a portrait of a young man by an unknown painter. (National Gallery of Victoria)

A painting owned by the National Gallery of Victoria in Melbourne has been identified as a portrait of Lucrezia Borgia, an infamous figure of the Italian Renaissance.

The oil painting, purchased in 1965, was formerly called Portrait of a Young Man and was thought to be by a Northern Italian painter.

On Tuesday, however, the gallery announced it had discovered the painting was by famed Renaissance artist Dosso Dossi who lived 1486-1542.

Gallery paintings conservator Carl Villis conducted extensive research to reach the conclusion the work was by Dossi.

"If it is accepted for what we believe it to be, then it will be highly-significant because it will be incredibly rare," he said.

"We believe this to be the only formal painted portrait of Lucrezia Borgia."

He discovered that Dossi was one of the few Italian painters to create oval portraits and forensic tests revealed an unusual primer unique to the painter.

The curator also discovered that Dossi had painted a group of ovals between 1515 and 1520 in the Este court in Ferrara, where Lucrezia lived. Only a handful of high-born women would have been considered important enough to be painted at the time.

The Borgia family were known for their political scheming, and Lucrezia has a reputation a seductress and manipulator, perhaps undeserved.

She was the illegitimate daughter of Cardinal Rodrigo Borgia, later Pope Alexander VI, and became Duchess of Ferrara, a position where she proved to be an able administrator.

The gallery says there is evidence Lucrezia was of gentle disposition, unlike her scheming family.

There are several clues that the painting is of a woman, including the background of myrtle and flowers. The dagger may be reference to an earlier Lucrezia, who took her own life after she was raped.

"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," Villis said.

"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."

Curators around the world have taken an interest in the painting since Villis made his discovery.

The gallery refused to speculate on the value of the painting.

With files from the Australian Broadcasting Corp.