The Fourth Apprentice is the first of six novels in the fourth arc titled Omen of the Stars in the Warriors series. Written by Erin Hunter and published on 24 November 2009, the book originally was to have been entitled Ambush. The Fourth Apprentice was originally the title of the fourth arc, but it was assigned to the first book; the fourth arc was then given its current title, Omen of the Stars.
The name of the fourth apprentice, rumored to be Dovekit or Ivykit, Whitewing's children, was revealed at the end of Sunrise. Jayfeather reveals that even though Hollyleaf was killed in the tunnels, Cloudtail is also Firestar's kin, and that the prophecy is still in play. This implied that the next book, The Fourth Apprentice, would reveal that one of the two daughters of Whitewing were to be part of the prophecy.