Only one Bach!
The King next requested him to play a six-part fugue, and Bach extemporised one on a theme selected by himself. The King, who stood behind the composer's chair, clapped his hands with delight, and exclaimed repeatedly, 'Only one Bach! Only one Bach!' It was a visit replete with honours for the old master, and when he returned home he expressed his gratitude by writing down and elaborating the piece which he had composed on the King's theme, dedicating it to His Majesty under the title of 'Musikalisches Opfer' (Musical Offering), and sending it to Potsdam with a letter begging its acceptance.