Waverly

Waverly is the daughter of Buttercup and Westley and is mentioned in the 25th edition of The Princess Bride.

Birth Story
Waverly is Buttercup and Westley's daughter, introduced in Buttercup's Baby, (she is not present in the original novel, The Princess Bride). She's born via C-section after 50 hours of labor, thanks to something or someone that possesses Fezzik and guides him through performing the procedure. She and Fezzik form a close bond and spend most of their time together. Buttercup's Baby begins and ends with the madman kidnapping Waverly and throwing her off of a cliff, though Goldman notes in earlier introductions that Waverly and Fezzik (who jumps off after her) are saved from their fall by the miraculous appearance of a giant bird.

One Tree Island
The island one tree is protected by a whirlpool, which is known to have a reputation of people not going past it. The crew (Butter, Westley, Inigo, and Fezzik) managed to get past it and start a life on One Tree Island.