The epilogue to some later editions of the novel, notably the 25th anniversary edition, mentions a sequel, Buttercup's Baby, that was "having trouble getting published because of legal difficulties with S. Morgenstern's estate". This sequel seems to be just as fictional as S. Morgenstern's unabridged edition, though later editions actually reprint Goldman's "sample chapter".
The chapter consists of a disjointed assemblage of stories about the quartet's escape to "One Tree Island", and the eventual kidnapping of Waverly, Westley and Buttercup's daughter, by a skinless-faced "madman" who eventually throws her off a mountainside. The chapter ends with Fezzik, Waverly's appointed babysitter, leaping off the mountain to save her, and then cradling her to preserve her from the impact that seems certain to spell at least Fezzik's doom. Also noteworthy is a flashback to Inigo's past, his training as a swordsman, and his one-time romantic love interest.
The 30th anniversary edition of The Princess Bride included hints to the sequel's plot, and a promise to have the full version completed before a 50th anniversary edition (2009).
In a January 2007 interview, Goldman admitted that he is having difficulty coming up with ideas for the story:
MPM: I hear you're working on a sequel to The Princess Bride called Buttercup's Baby.
William Goldman: I desperately want to write it, and I sit there and nothing happens and I get pissed at myself. I got lucky with The Princess Bride the first time, and I'd love to get lucky again.
Read more about this topic: The Princess Bride