When Albus Dumbledore died in Harry Potter and the Half Blood Prince I’ve discovered that some fans, that have watched the movies only don’t understand why? Though, people who have read the books should know that this Hogwarts Headmaster made a point of finding out anything about Tom Riddle’s Jr. activities away from the famed school.

Albus Dumbledore even showed Harry some of his memories that showed what he had done to help Harry with his fight against Voldemort aka Tom Riddle Jr.

As even though Albus Dumbledore told Severus Snape that there were ways where Tom Riddle aka Voldemort could come back.

He wasn’t certain what Tom Riddle Jr. had done until Harry some years after handed him the diary way back in Harry Potter and the Chamber of Secrets.

As Dumbledore tells Harry that when he (Harry) had gone into detail about what happen in the Chamber, and this was years later when Albus was giving Harry private lessons he told Harry that the diary had behaved exactly like a horcrux should.

Then in Harry Potter and the Deathly Hallows Hermione had read out to Harry and Ron that the venom from a basilsk is one of the ways to destroy a horcrux.

Also, as Harry had killed the basilsk with the sword of Godric Gryfindor. The sword was then capable of being used to destroy horcruxes.

The headmaster also discovered the location of the Gaunts house where he found the ring that Tom Riddle’s Jr. grandfather (Marvolo) was wearing from the memory of a person who Albus Dumbledore had interviewed.

As this person from the Ministry of Magic was at the Gaunts house to issue a warning about using magic against Muggles.

However, perhaps Dumbledore didn’t realize until after he had put the ring on that the stone that was set in the ring was a deathly hallow, and this meant that the Gaunts were related to the second eldest Peverell Brother.

As he, (the second eldest of the three Peverell Brothers) was the one who received the stone from death and Tom Riddle Jr. aka Voldemort had turned the hallow into a horcrux which was also protected by a curse.

It is unclear what happened when Dumbledore found the ring.

Though as we can only speculate. He (Dumbledore) had somehow made it back to his office at Hogwarts. I’m also guessing that like Ron with the necklace that was made a horcrux that something happened with the ring, which is probably why Dumbledore, used the sword that was in the office, and he would’ve had Fawkes with him. As Fawkes helped Harry destroy the diary then Albus Dumbledore summoned Severus Snape.

The headmaster then asked Severus how long he had to live. As Severus could only slowdown the poison that was from the curse protecting the stone.

Then Albus agreed to take Harry to the cave with him. As the headmaster had located that too and there the headmaster had to drink a potion called The Draught of Living Death and this made the drinker relive their worst memory.

Then Dumbledore’s worst memory was when Grindelwald who he was friends with at the time. Or really more than friends, was attacking his (Dumbledore’s) siblings. As Grindelwald was using the same unforgiveable curse that put Neville’s parents in St Mungo’s for the rest of their lives.