Harry and Ginny begin dating, and Harry is the happiest he has been in a while. Slughorn attributes Harry’s dipping performance in Potions to his being “lovesick;” Harry has not dared retrieve the Half-Blood Prince’s textbook yet, worried that Snape will be on the lookout for it. Hermione suggests that the Prince may have been a girl, showing Harry an old newspaper clipping of a Hogwarts student named Eileen Prince, but Harry dismisses this theory.

Harry receives a note summoning him to Dumbledore’s office immediately. On his way there, he runs into Professor Trelawney, the Divination teacher, outside the Room of Requirement. Trelawney is the person who made the original prophecy about Harry and Voldemort, though she does not know this herself. At present, she had been trying to get into the Room of Requirement but heard a male voice celebrating before she was ousted from the room. Harry insists that she must tell Dumbledore, sure that it was Draco inside. In a conversation on the way to meet the Headmaster, Trelawney inadvertently reveals that her job interview with Dumbledore many years ago was interrupted by Snape. Harry knows that this was when she made the original prophecy and that a Death Eater had partially overheard it and told Voldemort, causing Voldemort to kill Harry’s parents and attack Harry.