WARSAW (AFP) ― Six letters written by 19th century composer and pianist Frederic Chopin, thought to have been lost since World War II, were Thursday revealed by the Polish museum dedicated to the musical icon.

Warsaw’s Chopin Museum said that it spent almost a decade trying to obtain the letters and dozens of other documents related to the composer after getting wind of them in 2003.

The paper trial remains shrouded in mystery, with the trove acquired from its undisclosed owners by a Mexico-based Pole who donated it to the museum.

The letters, due to go on display this week, date from 1845 to 1848, a year before Chopin’s death in France.

Chopin wrote them in Paris and Nohant in central France, birthplace of his companion the writer Amantine Dupin ― better known by her pen-name George Sand.

They were written in Polish and addressed to family members back in Poland.

“The letters were last displayed in public in Poland in 1932,” the museum’s curator Alicja Knast told reporters. “And they were last confirmed as physically being in Warsaw in 1939.”

That was the year that Chopin’s great-niece, Laura Ciechomska, died aged 77. She was responsible for a collection of documents related to her illustrious ancestor.

The same year, Nazi Germany invaded Poland, sparking World War II. Like many priceless Polish cultural artifacts, the Chopin collection went missing during the six-year occupation.

Besides the six letters, the documents revealed by the museum Thursday include letters from Jane Sterling, a Scottish admirer and pupil of Chopin, and the composer’s sister Ludwika Jedrzejewicz.

“In 2003, we received the first indication that the letters still existed, said Knast. “In 2009, we began moves to try to acquire them.”

The museum was helped by Marek Keller, a Polish art dealer who has lived in Mexico for four decades. He acquired them directly from their owners, who Knast said wished to remain anonymous.

The documents will be on display at the museum until April 25.

In the letters, Chopin not only described his daily life but also his cello sonata in G minor, Knast noted. Composed in 1846, it was one of only a handful of his non-piano works.

Chopin was born on March 1, 1810 in Zelazowa Wola, near Warsaw, to a French father and Polish mother.

Already a musical prodigy as a youngster, he fled his homeland amid an 1830 Polish insurrection against occupying Tsarist Russia.

He lived in the Austrian capital Vienna before moving to Paris. Having long had health problems, he died aged 39 on Oct. 17, 1849.

While his body still lies buried in Paris, his heart was later returned to Poland and rests in Warsaw’s Holy Cross church.

Sterling’s letters date from after Chopin’s death, and tell of efforts to preserve his musical heritage and personal items.

Sterling is thought to have ordered a unique death-bed photograph of Chopin, the discovery of which in Scotland was announced by a Polish collector earlier this month.