Musical jargon. The major key of a tune. A major is King Alfred, B major King Bob, C King Charles, D King David, E King Edward, and G King George. Minor keys are princes. Example: The next tune is a reel in King Alfred, going to King David in the B part.
KING, PRINCE
Meaning of KING, PRINCE in English
Slang English vocab. Английский сленговый словарь. 2012