Considering that Albus Dumbledore (Jude Law) and Gellert Grindelwald (Mads Mikkelsen) meet face-to-face in Fantastic Beasts: The Secrets of Dumbledore, it's likely both parties must agree to destroy the blood pact in order to fight each other freely. The first two Fantastic Beasts movies connected J.K. Rowling's Wizarding World storyline in the 1920s with the Harry Potter timeline, mainly through Dumbledore, who is rallying everyone around him in his war against his friend-turned-foe Grindelwald. The third Fantastic Beasts installment will see Grindelwald rise to unprecedented power and Dumbledore more motivated than ever to destroy the blood pact and end Grindelwald's reign of terror.
Fantastic Beasts: The Crimes of Grindelwald ended with Newt Scamander (Eddie Redmayne) handing Dumbledore the blood pact, which he stole from Grindelwald via Niffler. When Newt asks the Hogwarts headmaster, “Can we destroy it?” Dumbledore replies with a short «maybe.» Perhaps he doesn't know what it will take, but it's just as (if not more) likely that he knows but is unsure if his plan will work out. Harry Potter fans know that by 1945, the blood pact will be destroyed, as that is when Dumbledore defeats Grindelwald in a historical duel. But judging by the second Fantastic Beasts 3 trailer, it seems like Dumbledore and Grindelwald will destroy the blood pact sooner, as the trailer shows them dueling each other freely.
Related: Harry Potter: Why Dumbledore Always Gets Away With Putting Others In Danger
The Fantastic Beasts 3 trailer shows Dumbledore and Grindelwald not only openly fighting each other but discussing inside what looks like a diner. This can mean that, in order to destroy the blood pact, both parties must agree to it.
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