Dennis Brain was born in London on 17 May 1921. He was educated at St Paul’s School in Hammersmith where he studied piano and organ. Although his father allowed his young son to play a few notes on Saturday mornings as a treat, he was adamant that students should not take up the instrument in a serious manner until they had reached their teenage years when the teeth and the mouth embouchure were fully developed. At the age of sixteen he left school having won a scholarship in open competition, which enabled him to go to the Royal Academy of Music. Dennis studied the piano with Max Pirani and organ with G.D. Cunningham in addition to the horn with his father. Such was his progress that he made his professional début alongside his father in the Bach Brandenburg Concerto No. 1 as a member of the Busch Chamber Orchestra on 6 October 1938. The event caused much interest with favourable press comment. The following month he took part in his first recording session with the same orchestra accompanying Rudolf Serkin in Mozart’s Piano Concerto K. 449. It was another recording session in February 1939 when again he played alongside his father in Mozart’s Divertimento in D, K. 334 for two horns and string quartet with the distinguished Léner Quartet, that brought his playing to the attention of the producer Walter Legge (1906–1979) who would play a critical rôle during the years 1945–57.