The clue he received in the film was from Bellatrix, who was in a frantic frenzy when she thought her vault was broken into. He is ultimately able to identify the cup as a Horcrux because of his ability to hear the piece of Voldemort's soul contained within them, an ability which is not present in the books.
After witnessing Nagini kill Severus Snape, Harry collected a string of memories from the dying man. During a one hour ceasefire, Harry discovered that he was an unintended Horcrux from Snape's memories. In order to destroy Voldemort, he had to allow the Dark Lord to kill him.
In this book, Rowling reveals that Bellatrix is the guardian of Helga Hufflepuff's cup (though she is unaware that it is a Horcrux), which Voldemort has entrusted the Lestranges to keep in their Gringotts vault.
Harry knows from his conversations with Dumbledore that if a Horcrux is in the vault, it must either be the Hufflepuff cup or else an unknown object, so they have no choice but to look for the cup.
Why did Voldemort hide a Horcrux in Bellatrix vault?
Voldemort chose this vault as his Horcrux's hiding place due to the fact that, since his childhood, he envied the wizards who owned a vault, as he himself did not due to his orphan-status.
Harry Potter is the Final Horcrux | Harry Potter and the Deathly Hallows Pt. 2
How did Harry know Hufflepuff Cup was in Bellatrix vault?
The clue he received in the film was from Bellatrix, who was in a frantic frenzy when she thought her vault was broken into. He is ultimately able to identify the cup as a Horcrux because of his ability to hear the piece of Voldemort's soul contained within them, an ability which is not present in the books.
After the fall of the ministry, the death eaters would have discovered that Dumbledore intended for the sword to go to harry in his will - so Snape was ordered to hand it over to Bellatrix for protection. Snape gave them a fake and found a way to get the real one to harry.
This betrayal ultimately proved to be Griphook's own undoing, as he was murdered by Voldemort alongside the other Goblins who reported the Cup's theft to him and Griphook's death caused the Sword to vanish back into the Sorting Hat.
Still, any Horcrux would be far more vulnerable than the Sword of Gryffindor. If the sword were to be imbued with a soul fragment and therefore turned into a Horcrux, it would no longer be indestructible but vulnerable to Fiendfyre and basilisk venom—two substances it would have otherwise absorbed in its natural state.
At some point, Umbridge received a locket as a bribe from thief Mundungus Fletcher. The pendant was actually Salazar Slytherin's locket and was, unbeknownst to her, one of Voldemort's Horcruxes. Due to Umbridge's twisted nature, the Horcrux actually amplified her magical abilities.
Delphini was born in secret at Malfoy Manor in early March 1998 as the result of a liaison between Bellatrix Lestrange and Lord Voldemort. On 2 May 1998, both of her biological parents were killed in the Battle of Hogwarts.
Family. Snape's family background is mostly shown in flashbacks during the course of the last three novels. Snape was born to Eileen Prince, a witch, and Tobias Snape, a Muggle, making him a half-blood (hence the name, "Half-Blood Prince").
Did Voldemort realize Harry was a Horcrux after he killed him?
Voldemort wasn't aware of Harry being a pseudo-horcrux because he didn't plan it, and Harry didn't know either until Voldemort “killed” him, but he actually killed the piece of soul kept in him.
Dumbledore knew about Horcruxes. He knew how they were formed, what happened after that, etc. He probably got to know Harry was a Horcrux when he saw the Scar on Harry's forehead, but maybe he wasn't sure.
They know she's an impostor. They've been warned", so obviously the request for the wand was unexpected even to him. It's thus pretty safe to conclude that the real Bellatrix had reported her wand stolen and alerted Gringotts prior to the trio's attempted break in.
It also needed to be recovered "under conditions of need and valour". To fulfil these conditions, Snape deposited the real sword in a frozen lake in the Forest of Dean and used his corporeal Doe Patronus to guide Harry to the sword.
In the books, Voldemort placed the Sorting Hat on Neville's head and sets it on fire, enraged that the boy would dare defy him. A battle broke out between the survivors and remaining Death Eaters and Neville kills the snake in one swing during the commotion. With Nagini dead, Voldemort was all out of Horcruxes.
Honestly, Hermione knew Dobby was a lost case... nothing could have revived Dobby after the attack or she would have definitely helped Harry with Dobby considering she was the girl who started S.P.E.W(Society for the Elfish welfare) and fought for elf rights. There was nothing to be done at that point.
Why was Bellatrix mad about the Sword of Gryffindor?
Bellatrix Lestrange believed Harry had broken into her vault at Gringotts after realizing Harry had the Sword of Gryffindor. Griphook lied to Bellatrix, telling her that the sword Harry had was a forgery.
Why didn't Dumbledore give Harry the sword before he died?
Question number one: Why didn't Dumbledore just give the sword of Gryffindor to Harry instead of leaving it to him in his will? He knew even before his death that Harry would need the sword to destroy Horcruxes, and he must have known that the Ministry would not let Harry get the sword.
After the Wizards' Council was reformed into the Ministry of Magic, tighter restrictions were placed on the use of certain kinds of magic. The Imperius Curse was deemed by the Ministry to be Dark magic, and, along with the Cruciatus and Killing Curses, were declared "unforgivable" in 1717.
There is likely a good reason that the Sectumsempra is not an unforgivable curse. It's mostly because Sectumsempra is Snape's personal curse that he created. It is not a widely known or used spell, and it is one that he kept secret — which means it can't be added to the list since no one really knows about it.
