Duke Ellington's son Mercer wrote this song in 1942, at the age of 23. It was the product of the 1941 composer's strike, which prevented the elder Ellington from putting his own songs on the radio. At the time of the strike Ellington would also rely on help from pianist Billy Strayhorn.
Perhaps, speculates jazz historian Chris Tyle, this was simply a labor law loophole, and Duke carried out the arrangements after his son wrote the tune.
