A crucifixion by Peter Paul Rubens has been discovered in a Paris mansion. Until now, Christ on the Cross (1613) was only known through engravings. It was found last September by French auctioneer Jean-Pierre Osenat, who was preparing a private residence in Paris for sale.

The painting’s authenticity has been verified by Nils Büttner, chairman of the Centrum Rubenianum in Antwerp. Its provenance was also confirmed through X-ray imaging, pigment analysis, and other scientific methods. The work will be included in the next update Addenda and Corrigenda of Rubens’s catalogue raisonné.

In a paper shared with Artnet News, Büttner expressed his astonishment that a work of such quality could have gone unnoticed for so long. He noted that the painting once belonged to the French academic painter William Bouguereau (1825-1905), but it’s unclear if the artist was aware of its true significance.

The Rubens expert admired how “Christ is shown isolated, standing out brightly against an ominous, dark sky,” noting also how “in a painfully realistic manner, Christ’s upper body arches forward, its weight shown by the strain on the arms” stretched overhead. “Behind the green and overgrown rocky backdrop of Golgotha is a view of Jerusalem illuminated, but apparently under a rainstorm,” Büttner added. This kind of accuracy was very typical of Rubens.

The painting will go up for auction in November.