An unknown oil sketch by John Constable, one of Britain's best-loved artists, has been discovered at the Victoria & Albert Museum.
The painting, of trees underneath an unsettled sky, was found concealed beneath a lining canvas on the back of Branch Hill Pond: Hampstead, another work by the English Romantic painter famous for The Hay Wain.
Conservators at the V&A, which was given the remaining contents of Constable's studio by the painter's last surviving child, Isabel, in 1888, found the sketch while attempted to remove the lining on the reverse after it became loose.
The V&A, which will be putting the previously unrecorded oil sketch on display tomorrow, said that Constable, who died in London in 1837, probably painted the scene in the late summer of 1821 or 1822.
During the period, the artist, who is known for his English landscapes, painted a number of sketches featuring similar cloud studies and motifs.
Conservators Clare Richardson and Nicola Costaras found the preliminary oil sketch while preparing works for a major 2014 exhibition, Constable: The Making Of A Master.
The oil sketch, painted on canvas measuring 24.5 x 39.4cm, depicts a narrow clearing fringed by trees set against an unsettled sky with a brown cylindrical structure, thought to be a kiln, in the foreground.
Constable, who was more successful in France than England during his lifetime and is known for his paintings of the Suffolk countryside, was thrifty with materials and sometimes painted sketches on both sides of a support.
Experts believe that he painted the sketch outdoors in London's Hampstead, on canvas which was probably pinned to the lid of his paint box for support.
The V&A was given three Constable easel paintings, 92 oil sketches, 297 drawings and watercolours and three sketchbooks in 1888.
Next year's exhibition Constable: The Making Of A Master, will represent the English painter alongside Old Masters of classical landscape such as Jacob van Ruisdael and Claude Lorrain.
Mark Evans, senior curator of paintings at the V&A, said: "The recent discovery is a rare and enormously exciting event.
"Constable was thrifty with... materials and sometimes painted sketches on both sides of scraps of reused canvas.
"This scene painted on the reverse of another sketch had been concealed for well over a century beneath a lining canvas."
He added: "We're looking forward to displaying both oil sketches as part of the major Constable exhibition next autumn."