A new Van Gogh painting! "Sunset at Montmajour" was unwrapped Monday at a museum that is tooting its own horn, loudly.  It's a rarity, said the director of the Van Gogh Museum. Historic. Once in a lifetime.

"A discovery of this magnitude has never before occurred" at the Amsterdam museum, said Alex Reuger. 

So, what's it worth?

Paintings by Vincent Van Gogh are among the most valuable in the world. And this one was ambitious by Van Gogh's standards, Reuger said, given the canvas size, about 3 feet by 2 1/2 feet. It is the first full-size Van Gogh discovered since 1928.

Photos: 'Sunset at Montmajour' and other Van Gogh paintings

True, the Dutch master wasn't thrilled with it. He made reference to it in a few letters written the summer in 1888 that he created the work, according to an Associated Press report. He thought the painting -- of bushes, trees, sky -- was flawed.

The work languished in the attic of a Norwegian man who had been given bad information: It wasn't a Van Gogh. The museum painstakingly authenticated the painting, which now belongs to a private collector and will be on view at the museum beginning Sept. 24.

Experts at Christie's wouldn't go out on a limb to assign a monetary value to the painting. And a spokeswoman for Christie's didn't want to talk about what goes into evaluating such a work. But she did say that the auction house had sold four of the top five Van Gogh paintings sold at auction.

Among those is "Sunflowers," which Christie's sold in 1987 for just shy of $40 million. It is of comparable size to "Sunset at Montmajour."

-- "Portrait of Dr. Gachet," created in 1890, sold 100 years later for $82.5 million.

-- "Portrait de l'artiste sans barbe," also painted in 1890, sold in 1998 for $71.5 million.

-- "Portrait of Madame Ginoux," 1890, sold in 2006 for $40.4 million.

-- "Sunflowers," 1889, sold in 1987 for $39.9 million.

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