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."
"Islands in the Stream" was originally written by The Bee Gees as an R&B song. It was originally written by the brothers for Marvin Gaye, however it was recorded instead as a duet by Kenny Rogers and Dolly Parton with the Gibb Brothers also contributing vocals.