A landmark painting by Francis Bacon, shown in public only once, is hitting the auction block this spring with an estimate of $20 million to $30 million.

Today, Sotheby’s announced that the painting, Study for a Head (1952), from the artist’s renowned  “Screaming Pope” series will lead its sale of works from the esteemed collection of Seattle philanthropists Richard E. Lang and Jane Lang Davis. The works will be spread across the New York auction house’s Impressionist and Modern evening sale on May 14 and iran contemporary sale on May 17.

Grégoire Billault, the head of Sotheby’s contemporary art department in New York and a former researcher for the Francis Bacon estate, considers the work the best of the “Screaming Pope” series, and “one of the greatest paintings we have ever offered in my 20 years at Sotheby’s.”

“The painting contains all the elements of the artist’s best-known works from this period—broken pince-nez glasses, a purple mozzetta, and of course the reverberating scream—and draws inspiration from the works of Velázquez, Munch, and Poussin, as well as Bacon’s lifelong exploration of the human condition,” said Billault in a statement. “We greatly look forward to presenting the painting to collectors and admirers of Bacon’s genius around the world this spring.”

Francis Bacon. Photo: via Prezi.

The painting was one of six portraits made by the artist in 1952, and the only one still in private hands. (The other five are split between the Tate Britain and the Yale Center for British Art.) It has only been exhibited publicly once—in a 2006 exhibition at the Sainsbury Centre for Visual Arts, Norwich, which looked at Francis Bacon’s work in the ‘50s.

Originally acquired by critic and Jackson Pollock biographer Bernard H. Friedman in 1952, the painting was purchased by Richard Lang and Jane Lang Davis in the early 1970s, becoming a cornerstone in what is considered to be one of the most important collections of 20th-century art.

Alberto Giacometti, Le Couple (1927). Courtesy of Sotheby’s.

Other pieces from the collection being auctioned off in May include Alberto Giacometti’s 1927 sculpture Le Couple—one of his first ever exhibited—which is expected to go for somewhere between $900,000 and $1.5 million; Willem de Kooning’s painting Woman with Red Hair (1967), estimated at $350,000-$450,000; Morris Louis’s 1962 Stripe painting Number 21 ($400,000-$600,000); and Hans Hofmann’s View from the Balcony from 1964 ($500,000-$700,000).

Fortunately, Bacon’s masterpiece—and others from the Richard Lang and Jane Lang Davis collection—are going on public display before they are sold. Study for a Head will make the rounds at Sotheby’s galleries ahead of the sale, being displayed in Hong Kong through April 2 before traveling to Paris (April 8-9), Los Angeles (April 16-17), and New York, where it will open Sotheby’s newly renovated galleries on May 3.