A painting valued at $15,000 just two years ago is now expected to fetch up to $18 million at auction after being identified as the work of the Dutch master Rembrandt.

"The Adoration of the Kings" has been virtually unseen since the 1950s, when it first came to light.

It was acquired by collector J.C.H. Heldring in Amsterdam in 1955. His widow sold it to a German family in 1985, where it remained until it was sold by Christie's in Amsterdam two years ago.

At the time of the sale, Christie's attributed the biblical scene to the "Circle of Rembrandt," suggesting it had been carried out by a student or an artist close to the famous painter, and estimated its value at between €10,000 and €15,000 ($10,600-$15,800).

The monochromatic painting, which measures 9.6 x 7.3 inches (24.5 x 18.5 centimeters), was purchased by an anonymous buyer for €860,000 ($908,000) at the Christie's sale.

Although that was more than 50 times the painting's estimated value at the time, it is now expected to fetch millions more, after emerging as "a work of great significance" by the Dutch painter, according to a press release from Sotheby's.

After the anonymous buyer consigned it to Sotheby's, the auction house embarked on an 18-month research project to arrive at the painting's true attribution and value.

The examination, which involved x-rays and infrared imaging, as well as intensive discussions with leading Rembrandt scholars, led Sotheby's to conclude the painting is "an autograph work by Rembrandt." It now values the work at between £10 million and £15 million ($12.2 million-$18.3 million).

The auction house believes it was painted early in Rembrandt's career, around 1628, when he would have been about 22 and living in the Dutch city of Leiden.

A rare find

The vast majority of Rembrandt's works hang in museums around the world, and almost all of those that have come to auction over the past three decades "have been portraits or studies of single character heads," according to the Sotheby's release.

As such, "The Adoration of the Kings," which depicts the encounter between the Three Wise Men and the baby Jesus, is a "fantastic opportunity" in the art world, George Gordon, co-chairman of Old Master Paintings Worldwide at Sotheby's, told CNN.

In a phone call with CNN, he said: "I would say that it's particularly significant because it adds to our understanding of Rembrandt at this crucial date in his development and career, when he was clearly very ambitious and developing very quickly as an artist."

The earliest reference to the painting appears to be from the 1714 inventory of a collector in Amsterdam, Constantijn Ranst. It was then offered for sale in 1814 and again in 1822 -- after which it disappeared from view until the mid-20th century.

It was included in museum exhibitions and referenced as a Rembrandt work by leading Rembrandt scholars in the 1950s, but in 1960 German art historian Kurt Bauch, who only knew the painting from a black and white photograph, described it as a product of the Rembrandt School and omitted it from from the catalogue raisonné he was compiling. Thereafter, the painting was "entirely overlooked and completely ignored in the Rembrandt literature," according to Sothebys.

Gordon told CNN that those bidding at the Christie's auction in 2021 "must have thought it was much better than the description and that it might well be a Rembrandt."

Sotheby's close examination revealed a number of changes and revisions that Rembrandt made, including to the baby Jesus' halo and the Virgin Mary's headdress, according to the auction house.

"Very few narrative paintings by Rembrandt remain in private hands, making this an opportunity for a private collector or an institution that is as rare as it is exciting," Gordon said in the news release.

"This sophisticated painting is in equal measure a product of Rembrandt's brush and his intellect. All the hallmarks of his style in the late 1620s are evident both in the visible painted surface and in the underlying layers revealed by science, showing multiple changes in the course of its creation, and casting fresh light on how he thought," he added.

The painting is currently on show at Sotheby's in Hong Kong, after which it will travel on to New York, Los Angeles and London, where it will be auctioned on December 6.