Why does Harry Potter think rowena ravenclaw's diadem is the last horcrux?

Answer 1

Harry thinks the lost diadem of Rowena Ravenclaw is a Horcrux because Voldemort's only real home, like Harry, was Hogwarts and Dumbledore told Harry that Tom Riddle came and asked for a job at Hogwarts but knew that he had never had any intention to teach. Voldemort had chosen places that wee significant to him, like the cave. He also wanted power and the four founders of Hogwarts were the most powerful wizards at that time. He figured if he could get a hold of something that belonged to them it would be like he conquered them, if that makes sense.