SALZBURG, Austria - Having famous parents can be a mixed blessing, but Austrian musician Franz Xaver Mozart had it tougher than most.

Born months before Wolfgang Amadeus Mozart died in 1791, Franz Xaver spent his life trying - and failing - to step out of his genius father's shadow.

"A child that disappoints their parents ... will encounter disgrace and misery. Let these words be a warning to my lovely (son)," his mother Constanze wrote in 1801 to her nine-year-old son.

Her ominous note is one of many personal letters currently on display at the Mozart Residence museum in Salzburg, as part of an exhibition organized by the Mozarteum Foundation.

"History has sort of forgotten Franz Xaver but he's actually of big importance to us," Mozarteum curator Armin Brinzing told AFP in an interview.

"We owe it to him that so many original manuscripts from the Mozart family including handwritten compositions have survived and are accessible to the public, instead of being destroyed or spread all over the world."

Of the six children born to Mozart and Constanze, only Franz Xaver and his older brother Carl Thomas survived into adulthood.

While Carl Thomas became a government official, Constanze had much bigger plans for her other son.

After her famous husband's death, the widow decided that Franz Xaver "should become the second Mozart", Brinzing said.

From the age of 2 she hired some of the era's most eminent teachers, including Italian composer Antonio Salieri whose pupils included Franz Schubert and Ludwig van Beethoven.

Even more tellingly, she only addressed her son as Wolfgang Amadeus.

In fact, Franz Xaver himself would sign all his works with "Wolfgang Amadeus Mozart, son".

Immense pressure

Letters exchanged between Franz Xaver and his older sibling reveal that from an early age, Franz Xaver felt under "immense pressure" and was "not treated very well at home".

Aged barely 13, Franz Xaver gave his highly anticipated first public concert in a packed Vienna hall.

Critics praised his performance but also warned the boy not to rest on his laurels.

"May he never forget that although the name Mozart currently grants him some indulgence, it will place great demands on him later on," read an editorial in the Allgemeine Musikalische Zeitung, a key 19th-century music magazine also on display at the Residence.

At 17, Franz Xaver fled the parental nest and took a job as a piano tutor for a wealthy family in the Ukrainian city of Lviv, then part of the Habsburg empire.

He spent the next two decades teaching and performing across Europe, but his artistic output was small and generally failed to impress.

He died of stomach cancer in 1844 during a health retreat in the Czech town of Carlsbad, where he was also buried.

Even in death Mozart's spirit still looms large, with Franz Xaver's tomb stone carrying the inscription: "May his father's name be his epitaph, as his veneration for him was the essence of his life."

Agence France - Presse