Art restorers have discovered the figure of a devil hidden in the clouds of one of the most famous frescos by Giotto in the Basilica of St Francis in Assisi.

The devil was hidden in the details of clouds at the top of fresco number 20 in the cycle of the scenes in the life and death of St Francis painted by Giotto in the 13th century.

The discovery was made by Italian art historian Chiara Frugone. It shows a profile of a figure with a hooked nose, a sly smile, and dark horns hidden among the clouds in the panel of the scene depicting the death of St Francis.

Sergio Fusetti, the chief restorer of the basilica, said Giotto probably never wanted the image of the devil to be a main part of the fresco and may have painted it in among the clouds “to have a bit of fun”.

The master may have painted it to spite someone he knew by portraying him as a devil in the painting, Mr Fusetti said on the convent’s website.

Little is known about Giotto di Bondone, but he is generally considered the man who triggered the Italian Renaissance.

He was born in 1266 or 1267 in Florence, and lived until January 1337.

However, one of his contemporaries, Giovanni Villani, wrote that Giotto was “the most sovereign master of painting in his time, who drew all his figures and their postures according to nature”.

He revealed that Giotto was given a salary by the Comune of Florence “in virtue of his talent and excellence”.