Locked up in a Swiss vault, among many items in a family's private collection, the portrait of Isabella d’Este remained hidden from the world. The owners of the artwork likely did not know even know what they had on their hands.

But, after carbon dating and thorough analysis by experts, the portrait has been verified as a Leonardo da Vinci original, according to Italian newspaper Corriere della Sera's Sette magazine.

The da Vinci painting, which depicts noblewoman Isabella d’Este, is believed to be a final version of a chalk sketch of the same woman. Like the circa 1500 drawing, which is currently on display in the Louvre, the da Vinci portrait measures 61 by 46.5 centimeters (24 by 18 inches) and illustrates its subject in profile, the Agence France-Presse reports.

At the time, Isabella d’Este sought out da Vinci in order to have her portrait painted. For centuries, art historians assumed that da Vinci had merely sketched the Marchesa of Mantua and failed to complete a painting of his drawing -- or that the painting was lost.

However, if expert authentication is to be believed, it seems the painting was not lost, but hidden through the centuries.

Renown da Vinci expert Carlo Pedretti had a hand in the verification and told the Italian-language magazine that he has no doubt that the portrait is a work of da Vinci. He added that it may be take several months to confirm what aspects of the painting were contributed by da Vinci's students.

But another expert, the University of Oxford's Martin Kemp, has his doubts. The art historian told The Daily Telegraph that da Vinci favored wooden boards, rather than canvas, which the Isabella d’Este portrait is painted on.

Last year, another painting thought to be a da Vinci work was uncovered in a Scottish farmhouse. Experts have yet to reveal if the estimated 500-year-old portrait of Madonna and child is authenticate. But, if it is the real-deal, the painting could be worth more than $150 million.