I went to one of her first concerts in Canada. Amazing. I'm old school when it comes to this type of jazz. As a pianist myself, I WISH I WAS HER! I try to copy her style, but it's inimitable, like her own idol, Nat King Cole. And that smoky, delectable voice - sheer G-d given talent.
Louis takes the whole first chorus pretty straight, then Ella comes in with a 2nd chorus, which she does as a deliciously inventive jazz variation on the melody.
Then Louis ends the song with a half chorus on his trumpet.