A new character appears when former Hogwarts Potions master Horace Slughorn returns to replace Severus Snape, who takes over the Defence Against the Dark Arts post. Harry excels in Potions by using an old textbook once belonging to a talented student known only as, "The Half-Blood Prince." The book contains many handwritten notes, revisions, and new spells; Hermione, however, believes Harry using it is cheating. Through private meetings with Dumbledore, Harry learns about Lord Voldemort's orphaned youth, his rise to power, and how he splintered his soul into Horcruxes to achieve immortality. Two Horcruxes have been destroyed, and Harry and Dumbledore locate another, although it is a fake. When Death Eaters invade Hogwarts, Snape kills Dumbledore. As Snape escapes, he proclaims that he is the Half-Blood Prince–Harry's admired mentor is actually his hated enemy. It now falls upon Harry to find and destroy Voldemort's remaining Horcruxes and to avenge Dumbledore's death. In a 2005 interview with NBC anchorwoman Katie Couric, Rowling stated that [after the events in the sixth book] Harry has, "taken the view that they are now at war. He does become more battle hardened. He’s now ready to go out fighting. And he’s after revenge [against Voldemort and Snape]."