THE father and son team who broke historic Rosslyn Chapel's musical Da Vinci Code have done it again with another of the artist's riddles.
Stuart and Tommy Mitchell believe they have cracked another secret of the Renaissance genius, this time in Leonardo's famous portrait The Musician.
Art historians have remained baffled for centuries over the meaning of the work.
They have also puzzled over the writing on the piece of music held by the subject of the 1490 painting, believed to be Da Vinci's great friend Franchino Gaffurio.
Now Stuart and Tommy have used mirrors to reveal the words "agnus dei" and a musical score.
Once the score is fully deciphered, Stuart plans to incorporate it in one of his classical pieces. as he did with the notes he found in Rosslyn.
Stuart said: "I knew Da Vinci was very secretive about his work, with many of his notebooks written in mirror code.
"So I took the painting and flipped the image on my computer as if it was being held up to a mirror.
"I could clearly see the word agnus, and instantly realised Da Vinci was saying agnus dei, the lamb of God.
"Traditionally the lamb of God is a term associated with Jesus, the son of God, the sacrifical lamb who gave his life for us to be saved.
"But it could also be a reference to St John the Baptist.
"Da Vinci was fascinated by St John. There are references to him in many of the artist's paintings, and his portrait was Leonardo's last.
"Leonardo was a Grand Master of the legendary secret society the Priory of Sion, whose warrior priests were the Knights Templar.
"They were alchemists, astronomers and scientists who were supressed by a Church which feared their knowledge.
"I believe Da Vinci was sending a secret code, signalling those in the know, the ancient equivalent of the Freemason's handshake."
Stuart, 46, from Edinburgh, a renowned classical composer and pianist, was feted around the world in 2007 when he and his father Tommy, 79, a former RAF codebreaker, revealed the symbols at Rosslyn Chapel corresponded to musical notes.
The Midlothian chapel featured heavily in Dan Brown's best-selling thriller The Da Vinci Code.
Tommy said: "This latest finding is equally exciting and although we still have lot of work to do, it corresponds with what we already know about Da Vinci's fondness for secret code."
Stuart is now working on trying to find a piece of music which fits the musical notes found in the document being held in The Musician portrait.
He said: "I'm looking at Ut Queant Laxis, which was written by the scholar Paul The Deacon in the 8th Century to honour St John the Baptist, and have found several similar notes to those found in the portrait.
"We'd love to hear from other experts who may be interested in helping us."
The discovery has delighted art experts.
A spokesman for Mario Conti, the Archbishop of Glasgow and a keen patron of the arts, said yesterday: "This is fascinating. Leonardo has teased critics and art experts down through the centuries and he continues to do so today.
"The Agnus Dei is a prayer which would have been sung in Latin at important masses in the cathedral then, as it is now.
"And so it would make sense for the words to be deciphered as such."
Richard Demarco, one of Scotland's most respected art experts, said last night: "This is remarkable and uplifting.
"I've examined this portrait many times but never realised what was written on that bit of paper.
"It's fascinating to know what inspired the great genius mind of Da Vinci."
This makes me want to embed all kinds of secret messages in my music.