<P> The students return to school , where Dumbledore announces that Snape will be teaching Defence Against the Dark Arts . In the meantime , Horace Slughorn will resume his post as Potions teacher . Harry now excels in Potions , thanks to having received a used Potions textbook that once belonged to someone named `` The Half - Blood Prince , '' a mysterious former student who wrote numerous tips and spells in his Potions textbook that Harry uses to achieve superb results . After a class contest , The Half - Blood Prince 's tips help Harry win a bottle of Felix Felicis , more commonly known as `` Liquid Luck . '' Though Harry 's success pleases Slughorn , his newfound brilliance in potions angers Hermione , who feels he is not truly earning his grades and does not trust the Half - Blood Prince . </P>
what is half blood prince in harry potter
mysterious former student who wrote numerous tips and spells in his Potions textbook that Harry uses to achieve superb results