Yes he found it at the end of the last book, it was in the ravenclaw common room.
Rowena Ravenclaw's lost diadem
Five horcuxes remain after Harry Potter and the Half-Blood Prince: Ravenclaw's lost diadem, Hufflepuff's cup, Nagini (Voldemort's snake), the locket, and Harry himself.
Sadly, Hedwig had to die in Harry Potter and the Deathly Hallows.
No
the diary the, the ring, ravenclaw's lost diadem, the snake Nagini, the locket, hufflepuff's cup and Harry, himself
A diadem is a jeweled crown worn as a symbol of sovereignty. The diadem in the Harry Potter books is Rowena Ravenclaw's and it was believed that it bestowed apon the wearer incredible wit. It was stolen by her daughter a long time ago and was lost. This is why the diadem is refered to as "the lost diadem of Ravenclaw" In the last part of the book, Harry and his friends believe it is a horcrux and contains a piece of Lord Voldemorts soul. Voldemort cannot die without all the horcruxes being destroyed so therefore, Harry needs to destroy the diadem. The only problem is that it is lost.
The answer I believe is 'diadem'. In Harry potter, they are in search of ravenclaws lost diadem and it turns out to be a tiara
Nagini (voldemorts snake), the lost diadem of Ravenclaw and Helga Hufflepuffs cup.
Rowena Ravenclaw's lost diadem
Five horcuxes remain after Harry Potter and the Half-Blood Prince: Ravenclaw's lost diadem, Hufflepuff's cup, Nagini (Voldemort's snake), the locket, and Harry himself.
He had doubts at one point because the diadem had supposedly been lost centuries before Voldemort's time.
find it
Sadly, Hedwig had to die in Harry Potter and the Deathly Hallows.
Yes, Cho Chang did try and take Harry to the Ravenclaw common room to look for the Lost Diadem in Harry Potter and the Deathly Hallows however Ginny was unhappy about this and suggested that Luna Lovegood took him.
Harry Potter finds the Lost Diadem of Rowena Ravenclaw in the Room of Requirement after thinking "I need the place where everything is hidden." It was perched atop "a stone bust of an old man wearing a wig and a tiara! It's standing on a cupboard..."This information can be found in Chapter Thirty-One The Battle of Hogwarts in Harry Potter and the Deathly Hallows by J. K. Rowling. (Page 628 in the Scholastic edition.)
actually there are 7 horcruxes which are : Tom Tiddle's diary, Salazar Slytherin's locket, the lost Diadem of Ravenclaw, the Resurrection Stone, Harry Potter himself, Nagini (Voldemort's pet snake ), and Helga Hufflepuff's cup
He suspects but he isn't sure. Harry knows that all the founders of Hogwarts had items. He knew that Salazar's locket was a Horcrux and because Tom Riddle/Voldemort thought of Hogwarts as home it made sense to make them into Horcruxes. However, the diadem was 'lost' so Harry wasn't sure even Voldemort had found it until after reading Voldemort's mind he found out where it was and that it was a Horcrux.