A rare 15th-century Renaissance portrait by artist Piero del Pollaiuolo is set to go under the hammer during a cross-category auction at Sotheby’s in London on March 25. Portrait of a Youth depicts a young male sitter set against a blue sky background and is expected to fetch £4 million–£6 million ($5.5 million–$8.2 million). It will hit the block alongside Old Masters works and contemporary art.

The painting—the only known portrait by Pollaiuolo left in private hands—was once held in the same private collection as the one that included Sandro Botticelli’s Portrait of a Young Man Holding a Roundel, which sold for a record-breaking $92 million at Sotheby’s on January 28 during the house’s New York “Classic Week” series. The previous owner of the two works was Thomas Ralph Merton, a prominent scientist who worked with the British secret service in the 1930s and ’40s.

The painting was first recorded in the collection of Hertfordshire’s G. M. G. Wilshere. In October 1942, the work is said to have been sold to Mendelsohn Bartholdy, who purchased it at Sotheby’s when it was attributed to a painter in the Florentine School (Sotheby’s is still conducting research to confirm this record.) Eventually, the work passed onto Sir Thomas Merton in the 1950s. The last time it sold at auction was in 1985, when it left Merton’s collection and sold at Christie’s, which attributed it to another Italian artist, Cosimo Rosselli.

Pollaiuolo’s Portrait of a Youth and Botticelli’s Portrait of a Young Man Holding a Roundel once hung side by side in Merton’s study. His collection also included works by Hans Holbein, Lucas Cranach, Bartolomeo Montagna, and other Italian and Northern Renaissance, some of which are now in U.K. museum collections.

Though lesser-known today than his contemporary Botticelli, Pollaiuolo was among the top artists working in the 15th century. Together with his brother Antonio, he ran one of the era’s most advanced Florentine studios, making commissions for elite Italian patrons such as the Medicis.

Piero, who despite having being less prolific than his brother, completed important projects independently, the most prestigious of which was the cycle of six paintings representing the Virtues for the audience chamber in the Tribunale di Mercanzia in Florence in 1469. The works are now at the Uffizi in Florence.

“In Renaissance Florence the Pollaiuolo brothers, Piero and Antonio, made important innovations across multiple art forms, not least in the field of portraiture, and their workshop rivaled that of Andrea del Verrochio for importance and prestige,” Cecilia Treves, Sotheby’s head of research on Old Master paintings, said in a statement.

Today, few major works by Pollaiulo remain in private collections; most are held by museums. (A 1480 profile of an elite woman, for example, is owned by the Metropolitan Museum of Art in New York.) The last time a Piero portrait appeared on the open market was in 2012, when a 1470 drawing of a young man sold at Sotheby’s for $1.4 million, against an estimate of $300,000. The buyer was the Getty Museum in Los Angeles.

Like the drawing purchased by the Getty, the present work depicts its sitter posed frontally—which is rare for the era, since most commissioning portraits were done in profile. According to Sotheby’s, the sitter’s young age is also rare, and “may have been intended as an affirmation of dynastic hope.”

This past November, the work was reviewed by the Art Council England, a body of the U.K. government which examines art objects that may be valuable to U.K. public collections.

In a statement to the Secretary of State, experts argued to keep the painting in the U.K. because of its potential significance for Renaissance scholarship. “It is the earliest painting in a British collection to illustrate a moment of change in Florentine portraiture—the movement from profile to full-frontal depictions of sitters,” said an expert adviser in the statement. Despite experts’ objections, the painting was approved for export.

In Sotheby’s forthcoming auction, the work will be sold alongside examples by David Hockney, Arshile Gorky, and Edvard Munch, among others.