So Dumbledore knew all along that he must have split-- he suspected until "Chamber of Secrets", and then at the point where he saw what was clearly the remains of a Horcrux, in other words, the diary, he thinks, okay, there you go.
He finds out for sure immediately after Nagini's attack on Arthur Weasley. This night is significant in many ways. While Harry sleeps, he enters Nagini's mind.
He went into hiding, expecting Voldemort to either recruit or kill him to keep his secret safe. But Dumbledore had known about the Horcruxes for a while, and by 1997, Slughorn knew he knew.
He already had prior knowledge of Horcruxes beforehand. Let's look at Chapter 23 of Book 6 (HBP), the part where Dumbledore and Harry were looking at the real unadulterated memory of Slughorn.
He believed that Harry was the one person who was smart, courageous, and perhaps lucky enough to find and eliminate all the horcruxes.
Once Hermione knew about horcruxes, she obviously looked into them. Sometime during the camping journey when she was 17 and Harry's scar hurt , the connection made sense to her. She noticed how Harry acted more like Voldemort when the locker was on, while Ron had acted insecure and her emotional.
Voldemort intentionally made six Horcruxes, but when he used Avada Kedavra on Harry, he unintentionally created a seventh Horcrux. Instead of dying, Lily's love for Harry created a counter 'curse' known as Sacrificial Protection and saved Harry.
First of all, Dumbledore didn't reveal the secret of horcruxes to Snape because he didn't find it necessary. It wasn't his style to let out unnecessary secrets to people. Making horcruxes to fight horcruxes wasn't the plan.
One is that Severus Snape is a master of Occlumency and therefore a difficult target for Voldemort to see through. The second is that Harry himself was not able to block Voldemort, and therefore the overall plan between Snape and Dumbledore was too critical to risk its discovery.
Did Snape know about the Horcruxes? No. Which makes his reaction to “the plan” of “killing” Harry all the worse. He was more disgusted with the fact that he “wasted” his time “protecting” Harry than he was that Dumbledore was “callously” plotting Harrys death.
Dumbledore wonders if one of the remaining two Horcruxes belonged to Ravenclaw, since Gryffindor's only known relic, the sword, is safe in Dumbledore's office. Dumbledore believes that Nagini, the snake, is the sixth.
“Dumbledore didn't want to lose his wand at that point and Draco disarmed him. So that meant that the wand gave Draco its allegiance, even though Draco never knew it, even though Draco never touched it. “From that moment on, that wand gave its allegiance to Draco, and it wouldn't work as well for anyone but Draco.”
The Emerald Potion, also known as the Drink of Despair, is a mysterious potion which induces fear, delirium, and extreme thirst. According to Dumbledore, the potion cannot be penetrated by hand, vanished, parted, scooped up, siphoned away, transfigured, charmed, or otherwise made to change its nature in any way.
In the Harry Potter and the Deathly Hallows book, Dumbledore admits to Harry that he only offered him scarce clues towards Voldemort's demise because he was afraid that Harry's hot-headedness would overwhelm his good heart if he were to know everything too soon.
Additionally, when Harry touches the ring, there is a flash of images as the ring reacts to him, which Dumbledore explains as an identifiable trace of lingering Dark magic.
He has grown afraid of Harry's connection to Voldemort. Perhaps Voldemort, knowing Dumbledore's love for Harry, would possess Harry and provoke Dumbledore to kill him. So, Dumbledore attempted to avoid Harry throughout Book 5 for Harry's own good.
Similarly to Harry, Snape's patronus represents a person. In the memories he gives Harry before his death, Snape shows Dumbledore his patronus, using the form to prove his love of Lily Potter, Harry's mother.
A Professor at Hogwarts School of Witchcraft and Wizardry, Snape is hostile to Harry due to his resemblance to his father James Potter, who bullied Snape during their time together at Hogwarts. As the series progresses, Snape's character becomes more layered and enigmatic.
Giving the information to Professor McGonagall allowed for the risk that she would tell him too soon, which might have allowed the golden trip to work out the possibility that Harry would survive, which would negate the sacrifice.
There was also a belief that the caster of Avada Kedavra needed the willingness to commit murder for the spell to work. While it was difficult to master the Unforgivable Curses, Harry might not have had the ability or desire to use the Killing Curse since he valued all living things.
While Voldemort was thwarted by three eleven-year-olds, he did not die at the end of the book because something that isn't fully alive cannot be killed. Overall, Voldemort was desperate to get his hands on the Stone to restore his body, his power and to try to find a way to beat death.
Dumbledore was afraid that Harry may repeat his youthful sins of searching the deathly hallows for wizard dominance. he was afraid the untimely information would damage Harry's motive to destroy voldemort. moreover Dumbledore wanted to destroy the wand's power by planning his own death.
Draco Malfoy's mother Narcissa was cold, cunning and devoted to the Dark Lord. But she was also a mother, which meant she was willing to risk everything to make sure her son was safe. When Harry survived Voldemort's Killing Curse for the second time, Narcissa pretended he was dead so she could get to Draco.
The most likely reason why Lord Voldemort's nose disappeared and he devolved into such an evil-looking creature is that as he dabbled deeper into the Dark Arts, his appearance gradually became as distorted as what remained of his twisted soul.
While most fans agree that Harry is the unrefuted Chosen One, the final Deathly Hallows film (in particular) sways heavily toward highlighting a heroic Neville, revitalizing the debate regarding which boy is better suited for the iconic title. "The one with the power to vanquish the Dark Lord approaches ...