Amsterdam’s Van Gogh Museum is celebrating after an extensive testing procedure identified Vincent Van Gogh as the creator of a 125-year-old painting discovered in a Norwegian attic. According to the Associated Press, the discovery is the first of its kind in 85 years.

The painting, titled “Sunset at Montmajour,” was housed for years in the attic of a Norwegian art collector who had been told it was not authentic. On the contrary, the Van Gogh Museum announced that two years of “extensive research” using a variety of techniques including X-ray photos, computer analyses of the canvas, and a microscopic analysis of paint layers, concluded that the painting was in fact the real thing.

“We carried out art historical research into the style, the depiction, use of materials and context, and everything we found indicated that this is a work by Van Gogh,” the museum’s two senior researchers Louis van Tilborgh and Teio Meedendorp said in a statement. “Stylistically and technically speaking, there are a plenty of parallels with other paintings by Van Gogh from the summer of 1888. By means of research into literature and records, we were also capable of tracing the earliest history of the provenance of the painting.”

Based on available records and literature that include two letters written by Van Gogh that directly refer to the painting, “Montmajour” is believed to have been painted near the Montmajour hill near Arles, France, on July 4 of 1888, a timespan that Van Gogh Museum Director Axel Rüger describes as “the most important period of his life.”

In 1888 and 1889, Van Gogh painted several of his greatest masterpieces, including “The Sunflowers,” “Starry Night,” and “The Bedroom.”

Van Gogh wrote a letter to his brother Theo the following day in which he seemed to refer to the painting’s landscape: “Yesterday, at sunset, I was on a stony heath where very small, twisted oaks grow, in the background a ruin on the hill, and wheat fields in the valley. It was romantic, it couldn’t be more so, à la Monticello, the sun was pouring its very yellow rays over the bushes and the ground, absolutely a shower of gold. And all the lines were beautiful; the whole scene had charming nobility.”

“All research indicates: this work is by Van Gogh,” Rüger said in a statement. He added that the museum could not disclose any other details about the painting’s previous owners due to privacy concerns, other than to say it had been in a family’s private collection for several years. However, Tilborgh said that a “180” on the back of the painting suggests that it was part of Theo van Gogh’s collection as of 1890.

In an article in the upcoming issue of The Burlington Magazine, the Van Gogh museum's three experts, Louis van Tilborg, Teio Meedendorp and Oda van Maanen, wrote that Norwegian industrialist Nicolai Christian Mustad had likely purchased "Montmajour" in 1908, at the urging of art historian Jens Thiis. According to a family anecdote, Mustad was content with his purchase until he received a visit from France's ambassador to Sweden who, upon seeing the painting, told Mustad that it was likely either counterfeit or had been mistakenly attributed to Van Gogh; ashamed, Mustad hid it in his attic.

There is some debate over who actually told Mustad that the painting was probably inauthentic. The article's authors take the view that it was likely not the French ambassador, but perhaps Auguste Pellerin, a Norwegian consul and prodigious art collector, who was also business rival of Mustad's.

"The art world was jittery at the time, possibly because of a rise in the number of forgeries in circulation, and as a result owners felt uncertain," the authors write of Mustad's fear of having purchased a fake. "Banishment was permanent; he never wanted to see the landscape again, and later photographs of his home confirm that it didn't hang among his other pictures."

An art expert's subsequent evaluation of "Montmajour" after Mustad's death in 1970 turned up the same conclusion: the painting was a fake. Two further requests to have it examined by the Van Gogh Museum also resulted in rejections, the Guardian reported.

In a press release published on Monday, the museum said the Van Gogh painting would be added to its public collection on Sept. 24. "A discovery of this magnitude has never before occurred in the history of the Van Gogh Museum. It is already a rarity that a new painting can be added to Van Gogh's oeuvre,” Rüger said. “But what makes this even more exceptional is that this is a transition work in his oeuvre, and moreover, a large painting from a period that is considered by many to be the culmination of his artistic achievement, his period in Arles in the south of France.”

In an interview with the New York Times, James Roundell, an art dealer specializing in Impressionist art, speculated that if the Van Gogh painting ever went on the market its taking price would likely be “in the tens of millions and quite a few of them.”

“One or two early van Goghs do sometimes come out of the woodwork now and again, but from the mature period it’s very rare,” Roundell said.

Meedendorp added that the investigation had “found answers to all the key questions, which is remarkable for a painting that has been lost for more than 100 years."