"I Didn't Know About You" is a song composed by Duke Ellington, with lyrics written by Bob Russell.[1] Recorded in 1944 with vocal by Joya Sherrill, it was based on an instrumental first recorded by Ellington in 1942 under the title "Sentimental Lady".
The recording by Count Basie & His Orchestra (vocal by Thelma Carpenter) briefly reached the No. 21 position on the Billboard charts in 1945[2] and other recordings available that year were by Duke Ellington, Mildred Bailey, Jo Stafford and Lena Horne.[3]