Oslo, Norway - Norway's National Museum has uncovered the secret behind an inscription on Edward Munch's original painting of The Scream, one of the most famous works of art in the world

Someone wrote in Norwegian "Can only have been painted by a madman!" in pencil in the top left corner of the famed canvas, which was completed in 1893.

"It is easy to imagine an indignant viewer, when faced with The Scream, taking a pencil and expressing their opinion on both the artwork and its creator. But that was not the case," the National Museum wrote on its website on Monday.

Instead, new analyses using infrared technology have found that Munch himself wrote the words.

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During conservation works after the museum closed, the painting was examined extensively in preparation for the reopening in 2022. Researchers said they had established beyond doubt that the handwriting matched that of the artist.

Munch's exhibition of The Scream prompted his peers to question his mental health at the time.

"The inscription can be read as an ironic comment, but at the same time as an expression of the artist's vulnerability. Writing on the finished painting shows that creating for Munch was a continuous process," said Mai Britt Guleng, curator at the National Museum.

Munch painted four versions of The Scream. The most well-known versions include the original and a later painting from 1910.