It's revealed in Fantastic Beasts: The Crimes of Grindelwald that Albus Dumbledore and Gellert Grindelwald created a Blood Pact when they were younger, and it's theoretically possible that the Blood Pact could be destroyed by using dragon's blood, something that Dumbledore is known for discovering in the Harry Potter franchise.
Throughout Fantastic Beasts 2, Dumbledore refuses to go after Grindelwald, and it's only later revealed in The Crimes of Grindelwald's ending that the reason the two couldn't fight each other is because their Blood Pact prevented it. Fans have known for a while that the Fantastic Beasts series is building up to the legendary duel between Grindelwald and Dumbledore, but now we are really starting to see these two great wizards come to the forefront.
We're also discovering some new lore about their magical battle, including the fact that Dumbledore and Grindelwald made a Blood Pact when they were young... and this pact has to be broken before Dumbledore can take him down. But the big question here is: can Dumbledore even break the Blood Pact? And if so, then how?
- This Page: The Blood Pact & Why Dumbledore Can't Break It
- Next Page: How Dumbledore Can Break The Blood Pact
The Blood Pact In Fantastic Beasts 2
Dumbledore's role in Fantastic Beasts: The Crimes of Grindelwald isn't as large as that of Grindelwald himself, but he does have a few very important scenes where we learn a little more about his history with the Dark Wizard (and his time as a teacher at Hogwarts). Throughout Fantastic Beasts 2, we see Dumbledore being approached by the Ministry of Magic, and asked to take the fight to Grindelwald, which he refuses... every time. He simply shakes his head sadly and says he can't, thus leading fans to believe that he simply still cares too much for Grindelwald to be able to fight him. Obviously, the Ministry is led to believe the same, which causes them to become very suspicious of Dumbledore, believing that he may still be sympathetic to Grindelwald's cause.
However, we learn toward the end of Fantastic Beasts 2 that Dumbledore's reticence isn't about his love for Grindelwald, but about a literal inability to "move against him" thanks to a Blood Pact that the two of them made when they were close to each other. We see him, looking into the Mirror of Erised, where he sees the two of them cutting their palms with wands and clasping hands, as a drop of their co-mingled blood is magically enclosed in a vial. This, like an Unbreakable Vow, is a spell that cannot be undone or gone against, which is why Dumbledore has Newt working for him, and Grindelwald has recruited Credence for his own side.
Dumbledore Can't Break The Blood Pact (Yet)
We know that, eventually, the Blood Pact between Dumbledore and Grindelwald is broken - because they have their legendary duel in 1945. However, in 1927, Dumbledore is unable to get around the vow he made as a youth to never fight the boy he loved. However, Dumbledore is one step closer to breaking the pact, because Newt used a Niffler to steal the magical vial from Grindelwald, who used to keep it on his person at all times. So now Dumbledore has the vial, and he can get to work on breaking it - although, given the dates of the film and his duel, it's going to take him some time.
We don't know a whole lot about Blood Pacts so far, because this is brand new lore J.K. Rowling has created for the Fantastic Beasts franchise, but we can make some educated guesses. In many ways, this spell appears to be similar to an Unbreakable Vow - with a few tweaks. For one thing, the Blood Pact can be made without a Bonder (a person to build and set the spell), whereas when Narcissa and Snape made the Unbreakable Vow in the Harry Potter series, Bellatrix had to act as Bonder for them.
For another, breaking the Unbreakable Vow simply ends in death, whereas it would seem that if a wizard can break the vial of the Blood Pact, the pact itself will be broken. We don't know if there will be any repercussions to breaking the pact, though - all we can surmise from Fantastic Beasts 2 is that the pact makes it physically impossible for either wizard to move against the other, and that the vial is the key to the pact. However, this is powerful magic, and at the time of Fantastic Beasts: The Crimes Of Grindelwald, Dumbledore doesn't know if it will even be possible to break it.