By: Andrew Lou

One of these hidden self-portraits was discovered at the National Galleries of Scotland.

“Moments like this are sporadic,” Frances Fowle, senior curator of French art, said in a statement. “We have discovered an unknown work of Vincent Van Gogh, one of the world’s most important and popular artists.” When Vincent Van Gogh did not have enough money to buy many canvases, he took to painting on both sides of the canvas that he used, but he usually covered up his reverse side painting, which was lost.

The portrait was revealed when the museum was preparing for an upcoming impressionism exhibition and X-rayed an 1885 Van Gogh, Head of a Peasant Woman.

“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.

Experts at the museum believe that materials were covering the hidden portrait in the early 20th century before the art was displayed.

“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 is something extraordinary.”

It’s not yet clear if it is possible to uncover the portrait, but that doesn’t means people can’t see it; the X-ray image shows a “ghostly” Van Gogh that people can see.

It isn’t the first hidden painting of his and might not be the last one. Others have been found previously, including one at the Van Gogh Museum in Amsterdam. Van Gogh is also known to have painted over his work sometimes. Who knows what other surprises may be in store?