Linda Entwhistle is Simon Belmont's girlfriend, according to the children's novel Worlds of Power 4 - Castlevania II: Simon's Quest. In this book, she was Simon's beloved and was captured by Dracula during the events of Castlevania. Simon defeated Dracula, but he realized things were not over when his love did not return to him. The same minions of Dracula who had separated his body parts, also kept Linda as a prisoner. She was still able to communicate with Simon through a vision, and warn him of the curse that Dracula had placed on him, also telling him how to overcome it. At the end of the novel, Simon, with the help of the eighth grader from our world, Tim Bradley, finally rescues his love.
Linda Entwhistle can be considered a combination of Selena from Haunted Castle (who was kidnapped prior to his quest), and the Mysterious Woman from Simon's Quest, who told Simon about his curse and what he must had to do to overcome it. The main difference between her and Simon's bride from Haunted Castle is that his bride was returned to him at the end of that game. Simon's Quest does not make any mention about the possibility of the Mystery Woman and Simon having any previous or future history together. Her name can be used for either of these two nameless characters by the fan community.