21–23 (K. 575, 589, 590), nicknamed 'Prussian', composed by Wolfgang Amadeus Mozart between 1789 and 1790 and dedicated to the King of Prussia, Friedrich Wilhelm II.
While Mozart was composing these quartets he was also working on a set of sonatas for the King's daughter, Princess Friederike (K. 576 was the only one completed).
In effect Mozart withheld the dedication and engraved the piece at his own expense as he wrote in a letter to his friend and fellow freemason Michael von Puchberg: "...
"[2] Mozart never dedicated the pieces to the Prussian King, so the title of these quartets has originated from his private 'thematic catalogue' of his own work (which he was keeping at the time).
These quartets are one of the estimable works of the composer Mozart, who was torn untimely from this world; they flowed from the pen of this so great musical genius not long before his death, and they display all that musical interest in respect of Art, Beauty, and Taste, which must awaken pleasure and admiration not only in the amateur but the true connoisseur also.