Painting of artist’s rural retreat, unseen in exhibition since 1895, will now go on show at National Gallery

Tracking down lost works of art usually involves poring over obscure documents in galleries, archives and libraries, searching for clues. But the curator of a forthcoming National Gallery exhibition on Claude Monet will be featuring a “missing” painting that he found through a startlingly straightforward route – a Google search.

The art historian Richard Thomson knew the painting, Effet de Brouillard, from a postage stamp-sized image in the definitive catalogue of works by the impressionist master. It was listed as being in a private collection.

Thomson, who is Watson Gordon professor of fine art at Edinburgh University, told the Observer: “It’s a picture that’s been off the beaten track, off the radar, and we’re going to have it in the show. Its whereabouts weren’t known… It’s exciting.”

Effet de Brouillard is an atmospheric scene that depicts Argenteuil, near Paris, the rural retreat where Monet lived between 1871 and 1878. It was here that he produced some of his most sublime masterpieces. Thomson thought that the 1872 painting, a hazy view of houses shrouded in fog, would be perfect for his exhibition, Monet & Architecture. He had already secured loans from private and public collections, and this seemed like a missing piece in the jigsaw.

To his astonishment, some Googling revealed that the painting had just been sold in America, by a New Orleans dealer. Art historians had apparently also missed its 2007 sale by Christie’s, whose catalogue entry notes just three previous exhibitions, in 1874, “possibly” in London, and in 1895, in Boston and New York.

The New Orleans dealer put Thomson in contact with the new owners, who were happy to see their painting displayed in the National Gallery.

According to Thomson, the work was featured in Paul Hayes Tucker’s 1982 book Monet at Argenteuil, in black and white, and in a 1990s catalogue in colour, where it was “only the size of a Christmas-card postage stamp”. He joked: “I’ve done my time buried away in archives and libraries. Every now and then one has to use other options.”

Effet de Brouillard will be among 75 works in the National Gallery exhibition, which opens in April. It will include 10 paintings of Argenteuil and the Parisian suburbs, seven Rouen cathedrals and eight London paintings.

A substantial proportion of the loans – about a quarter – are from private collections. “There are some fantastic unknown pictures,” Thomson said.

The exhibition will reflect how, through buildings, Monet explored “the play of sunshine, fogs and reflections”. As the artist put it in 1895: “Other painters paint a bridge, a house, a boat … I want to paint the air that surrounds the bridge, the house, the boat – the beauty of the light in which they exist.”

While Monet is typically portrayed as a painter of landscape, of the sea, and in his later years, of gardens, an exhibition focusing on his work in terms of architecture had not been undertaken until now, the National Gallery said.

The artist is a huge draw for the public. The Royal Academy’s 1999 blockbuster show, Monet in the 20th Century, attracted more than 700,000 visitors.