Seventh Son of a Seventh Son is the seventh studio album by Iron Maiden released on 11 April 1988. It is the first album in Iron Maiden's career to feature keyboards. Like The Number of the Beast and, later, Fear of the Dark, The Final Frontier and The Book of Souls, it debuted at No. 1 in the UK Albums Chart. It also marks the first appearance of many progressive rock elements which would be used frequently in later albums, seen in the length and odd time signatures of the title track "Seventh Son of a Seventh Son", and by the fact that it is a concept album.