A gauzy 17th-century portrait of a young man that a Dutch art dealer bought from Christie’s for just £137,000 ($172,000) is now being hailed as the first previously unknown painting by Rembrandt van Rijn to appear in nearly half a century. It is now on view at the Hermitage Museum in the Dutch Master’s hometown of Amsterdam for a brief celebratory run.

The Amsterdam-based dealer Jan Six acquired the portrait, an undated and unsigned oil painting attributed to the “Circle of Rembrandt van Rijn,” at a Christie’s London Old Masters Day Sale in December of 2016. Now, after a period of study, Six has lined up 15 curators and art historians in the Netherlands and abroad who vouch for the painting’s authenticity as a Rembrandt. It also has the seal of approval from professor Ernst van de Wetering, known for the Rembrandt Research Project and widely considered the world’s foremost authority on the painter.

For the dealer, a hunch paid off—in spades. “When I saw the catalogue it felt too good to be painted by someone from the circle of Rembrandt,” Six told artnet News. “The portrayed young gentleman really looks back at you; something very few artists are capable of painting.”

Rembrandt’s portrait of Jan Six in the “Dutch Portraits” exhibition at the Mauritshuis museum in The Hague in 2007. Photo by Rick Nederstigt/AFP/Getty Images.

A descendent of the Amsterdam mayor of the same name who was painted by Rembrandt in 1654, Six runs Jan Six Fine Art, a gallery specializing in Old Master paintings, with a particular focus on Dutch and Flemish paintings from between 1400 and 1800. His experience with the art of the period tipped him off to the painting’s special qualities.

“Lots of great details gave away that Rembrandt was the artist,” he said. “Observe the curling of the lace ruff at its edges, you can almost put your finger under it! For me that was a clear giveaway, as none of Rembrandt’s contemporaries could pull this off.”

Portrait of a Young Gentleman measures 39.8 by 29.3 inches and is thought to have been painted around 1634, when the artist was 28 years old. It depicts a young man in a black velvet coat with an ornate white lace collar and leather gloves, and is possibly part of a larger double portrait. The pre-sale estimate of the then-unidentified painting had been just £15,000 – £20,000 ($20,000 – $27,000) when it was sold at Christie’s.

“Within the field of Old Masters attributions can change,” a Christie’s spokesperson told artnet News. “We are aware that this work has been the subject of very lengthy further deliberation and analysis, subsequent to the sale, which we have yet to see.”

Employees carry Portrait of a Young Gentleman by Rembrandt van Rijn in The Hermitage Museum, Amsterdam on 16 May 2018. Photo by Koen Van Weel/AFP/Getty Images.

Six told artnet News that having the painting authenticated by Van de Wetering was one of the best moments of his career: “Ernst van de Wetering once taught me briefly at the university, and now I have written a book on Rembrandt with his consent! Wow!”

The book in question, Rembrandt’s Portrait of a Young Gentleman, launches today, and copies can be bought in Dutch and English at Amsterdam’s Hermitage Museum, where Six has agreed to show the painting until June 15.

After the painting has finished its run at Hermitage Amsterdam, Six tells artnet News he intends to sell it through his gallery, although he declined to share even a ballpark figure for the painting that could likely command millions. Rembrandt’s signed Portrait of a Man With Arms Akimbo (1658) sold for £20,201,250 ($33,258,562) at Christie’s London in 2009, the artist’s highest price at auction, according to artnet’s Price Database.