This was originally recorded by Nektar in 1972 for their album A Tab in the Ocean. Maiden's version was actually a mix of two of Nektar's songs, this and "Crying in the Dark." Because "King of Twilight" was more prominent, they also made it the title of the track. Steve Harris listened to Nektar a lot before starting Maiden.
This was used as the B-side to the single of "Aces High."