Composer and music historian Letho Kostoglou has made history, as the first Australian to complete Mozart's 'Great Mass in C Minor K 427' in full, traditional style.
The unfinished masterpiece known commonly as the Great Mass, was partly composed by the legendary Wolfgang Amadeus Mozart in Vienna, between 1782 and 1783.
Clayton Bay man and self-described Mozart scholar Mr Kostoglou, now joins a select group of around a dozen composers worldwide, who have "filled in the gaps" to fully complete the legendary work in the style of Mozart, and conclude it with a "12 bar sketch to the donna nobis pacem."
Having remained unfinished at the time of Mozart's death, the original Great Mass has large portions missing, which to complete in full to the standard and style of Mozart, requires decades of practice and a deep understanding of his works.
Mr Kostoglou who studied at the Elder Conservatorium of Music in the 1980s, before making a professional career in Sydney as a performer and composer, has spent the last 10 years finishing his version of the piece.
When performed, the Great Mass runs for about 80 minutes and requires two choirs and an orchestra; a combined ensemble of around 80 people.
At any one time, up to 20 'parts' can be playing at once, requiring a composer to map each section and instrument for the full performance; in this case over 267 pages.
Mr Kostoglou said he held a strong sense of achievement.
"I've always loved classical music and Mozart is the pinnacle for me," Mr Kostoglou said.
"I've listened to an enormous amount of Mozart music over the years and he was my late mother's favourite composer, so this is really special."
Having spent decades researching, training and developing a professional understanding of the work of Mozart, Mr Kostoglou previously spent a painstaking 16 years completing a composition of Mozart's unfinished 'Requiem Mass K 626', with the help of legendary Australian conductors Richard Bonynge and Patrick Thomas, in what was another Australian first.
"While working on the Requiem, I got to consult two greats in Patrick and Richard, who is also the husband of Dame Joan Sutherland the legendary dramatic coloratura soprano, who passed away in 2010," Mr Kostoglou said.
"Working alongside them, I got this great mentorship and my passion for Mozart has continued to grow."
Mr Kostoglou's version of the Requiem was performed at the Adelaide Town Hall in 2010, before he turned his hand to the Great Mass.
He has since dedicated his completed version of the composition to Dame Joan Sutherland, who performed the work twice in 1956.
Making the achievement even more special, Mr Kostoglou has received the seal of approval from his former mentor Richard Bonynge.
"I knew I'd done the best job I could, but hearing from Richard that he approved of the composition was praise indeed from a man who has spent his life conducting Mozart," Mr Kostoglou said.
"For him to allow me to then dedicate it to the memory of his wife really meant a lot to me."
The Great Mass is the only mass Mozart wrote with two choirs and was originally composed as part of a plea to God Mozart made, if he could marry his fiancée Constanze and take her to Salzburg to meet his family for the first time after his father's earlier opposition.
"Ultimately Mozart completed over half of the score, leaving the rest unfinished," Mr Kostoglou said.
"It's knowing how to fill in the blanks... you have to look at other works in a similar vein and rhythmic patterns in completed works, to see if you can then make sense of things harmonically.
"A fellow Aussie, Phillip Legge, did a damn good job previously, but to my knowledge he did not flesh out the final sketch.
"It's painstaking research; you have to know Mozart's style and try to get to know what he was thinking.
"This is very hard because unlike other composers, Mozart didn't wear his heart on his sleeve and was very guarded, but that's the genius of the man.
"We will never know how Mozart would have finished the Great Mass or his Requiem, but I would like to live in hope that the more people that do this, will inspire the next generation to keep researching and maybe uncover something that exists which is yet to be uncovered."
While Mozart's original Great Mass may be destined to remain unfinished, Mr Kostoglou hopes that might not always be the case.
"An additional sketch to Mozart's Requiem turned up in 1961 and just because we haven't found anything since then, it doesn't mean it doesn't exist," he said.
"Mozart wrote over 600 pieces of music, his genius was unrivaled and he changed music forever."
Mr Kostoglou is a trained concert pianist, accompanist and conductor and has performed on stage at the Sydney Opera House and in Germany.
Mr Kostoglou still performs locally and is hoping that one day, the Great Mass can be performed in Australia.