MADRID (AFP) ― Spain’s Prado art museum Monday unveiled a newly discovered jewel of French painting in which experts found a rare image of the historic French ruler Louis of Orleans.

When the Madrid museum received it from a private family in 2011, the 15th-century painting “Prayers in the Orchard” showed just Jesus and three apostles watched over by God in a starry blue sky.

But when experts scanned it and then removed layers of brown paint in the bottom left corner, they revealed a bald, red-haired nobleman in a red robe, accompanied by a female saint in green.

The insignia of golden nettle leaves on his sleeves identified the man as Louis of Orleans. The woman is Saint Agnes, a patron saint associated with his family.

It is one of only a handful of surviving pictures of the duke, and the only one painted on wood, said the museum, which called it “one of the most important finds in French primitive painting.”

Its fine quality and the rarity of works of its kind ― many of which were destroyed in the French Revolution ― make it “a little gem with great historical significance,” the Prado said in a statement.

“The great value of this work is that it is really unique,” said Maria Antonia Lopez de Asiain, who worked on restoring the painting for a year with a microsope and lancet.