Scientists say they have finally cracked a 500-year-old mystery – the secret of the Mona Lisa’s smile.

The enigmatic expression on Leonardo da Vinci’s most famous work was analysed by computer software, reports the New Scientist.

And the conclusion was that it conveyed 83% happiness, 9% disgust, 6% fear and 2% anger.

The conclusion was made after the painting, on view in The Louvre in Paris, was analysed at the University of Amsterdam.

The programme, co-developed with experts at the University of Illinois, drew on a database of young female faces to derive an average ‘neutral’ expression.

It then analysed features like the curvature of the lips and crinkles around the eyes to form conclusions about emotions.

But art expert Michael Daley argued: "The point of this work is that it’s a riddle – and the inaccessibility of the emotions on her face is why people are so fascinated by it.

"The idea that a computer can come up with four emotions to explain it is just ridiculous. Perhaps it’s possible with photos – but it is impossible with something created by the human hand."