Princess Boa is a character in the Abarat series by Clive Barker.
Boa was the daughter of King Claus, the last ruler of the Islands of Day. Until her death, Princess Boa is said to have been the Abarat's hope for conciliation between Day and Night, the two warring factions of the Abarat. She was set to marry Finnegan Hob; but was murdered on her wedding day by a dragon sent by Christopher Carrion, whose offer of marriage she had earlier rejected.
Although Candy does not know, Princess Boa is inside of her throughout the whole book, though she does not make an appearance.
It is finally revealed that shortly after her death, the Fantomaya transferred Boa's soul into the body of the unborn Candy Quackenbush, giving her the capacity to handle and perform magical abilities. This is what the prologue in Abarat is about.
Candy goes to the sorceress Laguna Munn and asks her to separate her soul from that of Boa. Laguna did as Candy asked her, but Boa proved to be malevolent and used Candy's body to aid her re-construction. Candy manages to stop her, and instead Boa uses the body of Laguna's younger son Jollo to reconstruct herself. Having reconstructed herself, Boa attempts rendezvous with Christopher Carrion; and failing that, with Finnegan Hob.