Mackerel Sky, which the famous British artist created in 1938, was reportedly last exhibited in 1939 when it was sold to a private collector.

The current owner loaned the piece to Hastings Contemporary, on Rock-a-Nore Road, which reopened yesterday (May 27) following the latest easing of lockdown restrictions.

The gallery announced last week that the ‘lost painting’ would appear in its new exhibition Seaside Modern: Art and Life on the Beach – a look at the popularity of the seaside among works by British artists from the 1920s to 1970.

Exhibition guest curator and art historian James Russell, who hosted a celebration of Ravilious watercolors at the Dulwich Picture Gallery in 2015, was contacted about the work in the spring of last year.

Speaking on Wednesday, he said: “Ravilious is now considered one of the most important artists of his time.

“Discovering a work from the peak period of his career – and a watercolor as wonderful as this one – is one of those moments that you lie in bed at night dreaming.

Mr Russell said he had been looking for “lost” works for about five years and it was “an important search for him personally”.

Speaking of the collector lending the work, he said: “It was by chance that this exhibition was going to see the light of day and they very kindly lent it.

“It fits perfectly – fishing boats, on the beach.

“It’s a wonderful, accessible kind of watercolor that anyone can enjoy, but it’s also a really beautiful modern work.”

Ravilious, born 1903, grew up in East Sussex and studied at Eastbourne College of Art.

He was a war artist during World War II and is known for his watercolors of the South Downs and other English landscapes.

He was declared missing in action in 1942, at the age of 39, after accompanying a Royal Air Force rescue mission off the coast of Iceland that did not return.

About 25-30 of his known works are believed to be missing.

Mr Russell said: “There are a few really intriguing ones and I’ve done some detective work over the years and tried to follow in the footsteps of where they might have been and not failed to find them. “

He added: “For something like this to come up is very exciting for me, and for British art of that time, it’s an important discovery.”

Mackerel Sky is signed and dated May 1938.

Mr Russell said Ravilious may have been in Tollesbury, Essex at the time.

“He painted several slightly similar images, but this is by far the best,” he said.

This is one of three Ravilious paintings on display as part of Seaside Modern – also Rye Harbor and Anchor, and Boats, both painted in 1938.

The exhibition, which was scheduled to be held last year but has been postponed due to the pandemic, features pieces by more than 60 artists – there are also works by LS Lowry, Barbara Hepworth and Paul Nash.

Speaking about the postponement and cancellation of exhibitions due to the pandemic, Mr Russell said: “I have been very fortunate that all of my work has been postponed rather than canceled.

“It opens just at the right time and is a celebration of the British seaside and its history, aside from being an interesting art exhibit.”

“I hope people like it. It’s a kind of uplifting exhibition. “

Seaside Modern: Art and Life on the Beach runs until October 31.