CNN_ An early work by British artist David Hockney, a painting depicting his well-known pool motif and not seen in public for more than 40 years, is headed for auction with an estimate of around $20 million.

Hockney, 86, painted “California,” showing two naked figures in an outdoor swimming pool, in 1965 after his first trip to Los Angeles and it has been held in a private collection since 1968.

The painting, last seen in public in 1979, is a highlight of auction house Christie’s “20th/21st Century: London Evening Sale” on March 7. It is listed with “a price on request,” with an estimate in the region of £16 million ($20.37 million).

“This is one of the earliest examples (of Hockney’s pool paintings),” Tessa Lord, a senior specialist and director of the post-war contemporary department at Christie’s London, told Reuters at a press preview on Thursday.

In 2018, Hockney’s 1972 piece “Portrait of an Artist (Pool with Two Figures)” sold for $90.3 million, setting a then record for the highest price ever paid at auction for a work by a living artist.

“There is a lot of crossover between the two works but also we’ve seen since that world record price in 2018 a real broadening of the market for David Hockney,” Lord said.

“We have sold works from the Paul Allen estate over the past few years, which in particular shone a light on his later practice, his landscapes and what we’re coming to feel is a real international recognition amongst collectors of Hockney’s contribution to 20th and 21st century art, and a real drive to seek out the best examples of his practice.”

“California” will go on a touring exhibition to Paris and New York next month before returning to London to go on public view before the sale.