there were altogether three recordings of this song by Nat King Cole:
1. the original 1951 (mono) recording, with an arrangement written by Nelson Riddle;
2. a second non-orchestrated version recorded in 1952, featured as a bonus track on the CD reissue of 1955's completely instrumental (save the bonus material) Penthouse Serenade;
3. 1961 stereo recording included in The Nat King Cole Story (1961), with Nelson Riddle's 1951 orchestral arrangement.
en: Unforgettable (Nat King Cole song) [info]