A collection of six letters written by revered Polish composer Frederic Chopin were donated to the Fryderyk Chopin Museum in Warsaw on Thursday. The letters were believed to be lost in 1939.

The collection was donated by Marek Keller, a Polish emigre art dealer. Mr Keller hasn't revealed from whom he obtained the documents.

The letters, written by the composer to his family between 1845 and 1848, were given as part of a collection of 47 documents related to the life of the composer and his relatives.

The memorabilia include, among other things, correspondence addressed to the relatives of the composer, manuscripts written by Chopin's sister and drawings of unknown authorship, which belonged to the composer.

Emphasizing that the letters are a priceless source of knowledge on Chopin's life, Alicja Knast, the curator of the museum, said at a Thursday press conference that, from the letters, one can discover more about the composer's last concert in Paris and the process of creating the g-moll Sonata.

Poland's Minister of Culture, Bogdan Zdrojewski, said during the press conference that efforts to acquire the collection were begun in 2009 by Alicja Knast, the curator of the museum. He explained that thanks to the joint effort of Ms Knast and Mr Keller the documents have become part of the museum's collection.

The letters, due to go on public display this week, will be viewable until April 24 in the Fryderyk Chopin Museum.