Fiona McLaren inherited this mysterious religious painting from her GP father but never realised its potential true value until she had it dated to the early 16th century.

Experts have confirmed its Renaissance provenance and Ms McLaren has put together compelling evidence to show it is by the greatest of all the Old Masters, Leonardo Da Vinci.

In 2012, she wrote a book called Da Vinci's Last Commission exploring the artwork's mysterious symbolism about Mary Magdalene and the secret bloodline of Jesus Christ.

Her story made headlines around the world and even led to a verbal offer of £150million for the painting from a Russian oligarch.

However, the sale fell through amid the chaos in the Ukraine and Ms McLaren continued with her quest to prove conclusively that her painting is the work of Da Vinci. 

After five years of tireless research from her home near Crieff, Perthshire, she has put together many more pieces of the extraordinary story.

And now she plans to sell the painting, safely kept in a bank vault, at auction next year to mark the anniversary of the Italian genius's death at the French royal palace at Amboise in the Loire Valley in May 1519.

Her hopes were raised by the record £340million sale in New York last year of the Salvator Mundi, whose attribution as a genuine Da Vinci has been the subject of heated debate.

Ninety per cent of any proceeds will go to setting up a global children's charity called the Caterina Peace Foundation after the teenage orphan now thought to have been Da Vinci's mother.

Ms McLaren said: "Leonardo died in 1519 and I want the Foundation to open in 2019 as a tribute to both his mother and to establish him as the greatest philosopher and philanthropist that ever lived.  

“If the Salvator Mundi sold for $400million then my painting must be worth at least that. 

“Just think what that money could do for children in need all around the world. 

“It would be a global charity based in Scotland."

The most intriguing new piece of evidence she has discovered is the existence of a possible sister painting in a gallery in Venice.

In 1506, Da Vinci wrote a letter promising to bring "two pictures of Our Lady" from Florence to Milan (then under French control) as a gift for his new patron, Louis XII.

These "two Madonnas of different sizes" have never been identified but Ms McLaren, 64, a former TV researcher, now believes her painting is one of them. 

And she is convinced the other is now part of the collection held by the Manfredi Gallery in Venice.

The Holy Family with a Musician Angel was previously attributed to Da Vinci but is now regarded as the work of one of his students, Giovanni Antonio Boltraffio.

The infant Jesus in the painting in Venice is virtually identical to the infant John the Baptist in Ms McLaren's painting, a similarity which has been independently agreed by experts from two auction houses.

Meanwhile, the bald figure bears a striking resemblance to the surviving images of Pope Julius II, the warrior pope who drove the French out of Italy.

Ms McLaren said: "I believe it is a caricature of Pope Julius which is why I believe this and my painting were gifts to Louis XII. 

“Pope Julius excommunicated Louis and was no friend of the king; he was known as the Fearsome Pope.  

“Moreover Leonardo had little time for him either."

She also suggests the two identical infants are in fact the young Louis XII, who was an ardent believer in the theory that the French royal family were descended from Christ and Mary Magdalene.

This would also explain the wealth of secret symbolism hidden in Ms McLaren's painting, including Hebrew letters, Kabbala mysticism, hidden faces in the clouds, Masonic hand symbols and Biblical imagery.

In both paintings the central figure has her head bowed at exactly the same angle as in some of Da Vinci's other works, including the Virgin of the Rocks.

Ms McLaren has also uncovered some remarkable geometry and mirror imaging in her painting, with her findings supported by Bulent Atalay, author of Maths and the Mona Lisa.

When a mirror is placed down the centre of the painting, the female figure's head fits exactly with the famous Fibonacci Spiral, the so-called Golden Mean found in much of Da Vinci's art. 

One of the biggest clues to the provenance of her painting is a genuine papal bull - or seal - on the back from Pope Paul V, who reigned from 1605 to 1621.

Since her book was published, Ms McLaren has had confirmation from the Vatican that her painting was indeed once held in the Secret Archives founded by Paul V.

Remarkably, the painting also has a rail freight ticket on the back showing that it was sent from Turin to Paris on the Paris-Lyon-Mediterranean railway in 1863.

It arrived at St Michel station on the Left Bank and then disappeared from history, until Ms McLaren's father brought it home one day in the early 1960s as part of a box of artefacts from a grateful patient.

The family were living in the suburbs of north London at the time and the identity of the patient died with George McLaren in 1979, although they may have had a connection to Freemasonry.

Ms McLaren is now raising funds for an expedition to Italy later this year, where she plans to visit the sister painting in Venice and have her own painting examined by the world renowned experts at Editech in Florence.