A hidden self-portrait of Van Gogh has been discovered. Here's what you can see so far

An X-ray image shows this previously unknown self-portrait of Vincent Van Gogh painted on the reverse side of his painting Head of a Peasant Woman. (Graeme Yule/National Galleries of Scotland)

When Vincent Van Gogh was low on money he took to painting on both sides of the canvas, but over the years some of his reverse side paintings were covered up and lost. Now, another of his hidden self-portraits has been discovered, this time at the National Galleries of Scotland.

"Moments like this are incredibly rare," Frances Fowle, senior curator of French art, said in a statement. "We have discovered an unknown work by Vincent van Gogh, one of the most important and popular artists in the world."

The self-portrait was revealed during an X-ray of an 1885 painting by Van Gogh, Head of a Peasant Woman, as the museum was prepping for an upcoming exhibition on impressionism, which is scheduled to open at the end of the month.

"Hidden from view for over a century, the self-portrait is on the back of the canvas with Head of a Peasant Woman and is covered by layers of glue and cardboard," the museum said in a statement on Thursday.

Van Gogh's Head of a Peasant Woman is one of three pieces of the artist's work in the National Galleries Collection. With the discovery of the hidden self-portrait, they now have four works in total. (National Galleries of Scotland)

Experts at the museum believe the materials covering the newly discovered self-portrait were applied in the early 20th century before the art went on display.

"When we saw the X-ray for the first time of course we were hugely excited. Such a major discovery happens once, twice in a conservator's lifetime," senior paintings conservator Lesley Stevenson said in a video released by the museum. "To have an image as elusive as it presently is something very, very special."

It's not clear yet whether it will be possible to uncover the hidden self-portrait, but that doesn't mean you can't see it. An X-ray image of the ghostly portrait will be part of the upcoming exhibit, viewable using a special lightbox.

The museum describes the newly discovered image as "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."

This self-portrait isn't the first hidden painting of Van Gogh's to be discovered and it might not be the last. Other double-sided works of Van Gogh's have been uncovered previously, including at the Van Gogh Museum in Amsterdam. The famous artist also painted over his work at times.