I’ve been wondering about that gleam of triumph for quite sometime.
First of all lets consider what Harry’s blood contains, traces of his mother’s sacrifice, which protected Harry from Voldemort’s killing curse and which made it backfire on the Dark Lord. I have read many different theories over the years on the various Harry Potter fan sites and editorials on mugglenet, some of which went along the lines of Dumbledore being evil.
Now, armed with the knowledge of the prophecy and what the power the dark lord knows not, I have formulated a rather bizarre cheese cauldron worthy theory, in which Dumbledore is not evil, but in which the gleam of triumph was yet another piece to the puzzle of how Harry may cause Voldemort’s final downfall.
We learn from Dumbledore in the Horcruxes chapter of the half blood prince, many interesting facts about Harry. That he is just as pure of heart as he was when he was 11 and looked into the mirror of erised and saw not immortality and riches, but the only way to thwart Lord Voldemort.
Canon evidence quote 1: ‘You are protected, in short, by your ability to love. Said Dumbledore loudly. ‘The only protection that can possibly work against the lure of power like Voldemorts! In spite of all the temptation you have endured, all the suffering, you remain pure of heart, just as pure as you were at the age of eleven, when you stared into a mirror that reflected your heart’s desire, and it showed you only the way to thwart Lord Voldemort, and not immortality and riches. Harry, have you any idea how few wizards could have seen what you saw in that mirror? Voldemort should have known then what he was dealing with, but he did not!’ Pages 477-478, chapter 23, the half blood prince, UK edition
Dumbledore goes on to say that because Harry’s soul is untarnished and whole it has incomparable power over what is left of Lord Voldemort’s mutilated soul.
Canon evidence quote 2: ‘But he knows it now. You have flitted into Lord Voldemort’s mind without damage to yourself, but he cannot possess you without enduring mortal agony, as he discovered in the Ministry. I do not think he understands why, Harry, but he was in such a hurry to mutilate his own soul, he never paused to understand the incomparable power of a soul that is untarnished and whole.’ page 478, chapter 23, The half blood prince, UK edition
We also learn that Harry’s power over Voldemort is just love (see quote 1). Perhaps one of the uniquely deadly weapons Voldemort handed Harry when the curse backfired.
Now if we take a look at Harry’s soul and his power to love where can it lead us? Back to the end of the order of the phoenix and Voldemort’s failed possession attempt on Harry.
Canon evidence quote 3: ‘If death is nothing, Dumbledore, kill the boy…’ Let the pain stop, thought Harry … let him kill us … end it, Dumbledore … death is nothing compared to this … And I’ll see Sirius again … And as Harry’s heart filled with emotion, the creature’s coils loosened, the pain was gone; Page 720, chapter 36, The Order of the phoenix - UK edition
We learn from Dumbledore in the lost prophecy chapter that Harry was saved from possession not because he could not close his mind, but because he opened up his heart about Sirius Black.
canon evidence quote 4: ‘In the end, it mattered not that you could not close your mind. It was your heart that saved you.’ Page 743, Chapter 37, Order of the Phoenix - UK edition
Fast forward to the Horcruxes chapter in the half blood prince and we learn from Dumbledore that Voldemort cannot possess Harry without enduring mortal agony, whereas Harry can flit in and out of Voldemort’s mind with little damage to himself.
The question i ask myself is why does Voldemort feel this mortal agony and Harry is undamaged?
Part of the answer is that Harry’s soul has incomparable power over what is left of Voldemort’s soul which is beyond repair, so perhaps that causes Voldemort’s soul to weaken.
The other part of the answer i think is to do with Harry’s ability to love.
Voldemort does not understand love and he could not touch Harry at the end of the first book, because he was protected by his mother’s sacrifice which was borne out of love for Harry. This is the blood that Voldemort used to regenerate his body and come back from whatever he was after his first fall from power. He is able to touch Harry without feeling any pain. But now i think when Voldemort possessed Harry at the end of the order of the phoenix, his assumption that using Harry’s blood would make him invincible is in reality yet another one of Voldemort’s miscalculations.
When Harry opened up his heart about Sirius i believe that not only did Harry’s soul cause Voldemort to feel mortal agony, the blood he shares with Harry, was influenced by that surge of love Harry had. This activated the latent protection Lilly Potter provided to protect Harry from Voldemort. So, in essence Harry can influence the blood that is circulating in Voldemort’s body to an extent that could possibly kill Lord Voldemort.
Hence, the gleam of triumph might have been Dumbledore seeing another piece of the puzzle of how to finish Lord Voldemort off falling into place. Nothing sinister, just another weapon in Harry’s deadly arsenal of talents and gifts that will help him bring about Voldemort’s final downfall.
Now this method of loving Voldemort to death would only work under a few conditions: 1. Voldemort’s Horcruxes would first have to be destroyed 2. Harry would have to allow himself to be possessed by Voldemort or force his way into Voldemort’s mind. 3. Harry would have to hold Harry in this deadly embrace until one of them dies.
As to the question of Harry being a horcrux, i think this theory would most likely still work. In essence Harry would have to use his connection via the scar to enter Voldemort’s mind, and then with his ability to love kill the last two remaining pieces of Voldemort’s soul. Without killing himself in the process. But it could work.
However i did say this is probably a cheese cauldron worthy theory. I’m probably not even barking up the right tree. But it all seems to fit into the grand scheme of things in relations to Dumbledore’s Gleam of triumph being the hinge on which the series is balanced on.