A powerful X-ray technique has unveiled a hidden portrait beneath a painting by French impressionist painter Edward Degas.

An article published this week in the online journal Scientific Reports reveals an image concealed behind Degas "Portrait of a Woman" is, in fact, a portrait of another woman. Australian researchers believe she is Emma Dobigny, one of the painter's favorite models.

Experts have long known that Degas painted the famed portrait over another image. As the painting aged, the faint outline of what appeared to be another woman began leaking through the top layers of paint.

Staff at the National Gallery of Victoria in Melbourne asked scientists from Australian Synchrotron to scan the painting with a high-definition X-ray beam produced by a particle accelerator called a synchrotron to unveil the image.