Horse Head, Jesus, Lamb

The discovery of three almost invisible drawings on the back of Leonardo da Vinci's Virgin and Child With Saint Anne in the Louvre museum in Paris have the French art world screaming "Sacre bleu!"

Reminiscent of Dan Brown's Da Vinci Code, the mysterious sketches were found by experts looking into restoring the sixteenth-century masterpiece.

They were detected when a curator noticed that some of the gray marks behind Virgin and Child With Saint Anne resembled a horse's head.

An infrared photo confirmed his suspicion and revealed two other sketches: a human skull and the infant Jesus with a Lamb.

Experts say Da Vinci had a habit of sketching on whatever was at hand, and might have used the planks of wood he used to form the backing for the work.

"This is an exceptional discovery as sketches on backs of works are very rare and there is no known example of one from Leonardo to this day," the Louvre said in a statement.