Ellington never ceases to amaze and suprise me. Witness this short piece, released by Storyville earlier this year: "The Lake", part of his suite "The River", and performed at the end of a 1969 concert. Here are the Storyville notes: 

"On November 7th, 1969, Duke Ellington and his orchestra played two concerts in Rotterdam, in the famous De Doelen concert hall. The second concert of the evening was prolonged, as the public wouldn’t let Ellington go. So while the rest of the bandmembers left the stage, a quartet with Duke, Wild Bill Davis, bassist Victor Gaskin and drummer Rufus Jones stayed, and played four more numbers, much to the delight of the sold-out house. You can hear the whole band concert on the Storyville CD “Rotterdam 1969” (1018440), and here we offer the ”afterparty” music by the quartet. "

Check it out ! 

https://storyvillerecords.bandcamp.com/track/the-lake