A self-portrait of Dutch post-Impressionist artist Vincent Van Gogh has been uncovered hidden behind one of his paintings.

National Galleries of Scotland said on Thursday that art conservators made the discovery, believed to be a first for a UK institution, during an x-ray examination of Van Gogh's 1885 artwork "Head of a Peasant Woman" for an upcoming exhibition.

It said the x-ray showed "a bearded sitter in a brimmed hat with a neckerchief loosely tied at the throat. He fixes the viewer with an intense stare, the right side of his face in shadow and his left ear clearly visible".

The image was hidden behind cardboard and layers of glue.

"When we saw the x-ray for the first time of course we were hugely excited," senior paintings conservator Lesley Stevenson said in a video shared by National Galleries of Scotland.

"Such a major discovery happens once, twice in a conservator's lifetime... To have an image, as elusive as it presently is, is something very, very special."

Van Gogh is known to have often re-used his canvases, working on their reverse as well.

National Galleries of Scotland said its experts were looking at how to remove the glue and cardboard covering the self-portrait without damaging "Head of a Peasant Woman".

The x-ray image will feature at the July 30-Nov. 13 exhibition, called "A Taste for Impressionism", at the Royal Scottish Academy in Edinburgh.