The third 'Fantastic Beasts' film answers a pivotal question about Grindelwald and Dumbledore that will make it possible for them to have a giant showdown in a future movie

• Warning: Major spoilers ahead for "Fantastic Beasts: The Secrets of Dumbledore."
• "Fantastic Beasts: The Crimes of Grindelwald" revealed that Dumbledore and Grindelwald can't fight each other.

The "Fantastic Beasts" series, despite being named for a magizoology book written by franchise lead Newt Scamander (Eddie Redmayne), deals primarily with the rise of Gellert Grindelwald, prior to his defeat at the hands of Albus Dumbledore in 1945.

The latest film has delved further into Dumbledore and Grindelwald than any other book or film in the "Harry Potter" franchise. The two rivals, and former lovers, are at odds in history, but the first two "Fantastic Beasts" films have made it impossible for them to fight each other just yet.

"Fantastic Beasts: The Secrets of Dumbledore" finally reveals how it's possible for Dumbledore and Grindelwald to have their giant showdown that ultimately ends in Grindelwald's imprisonment.

Warning: Major spoilers for "Fantastic Beasts: The Secrets of Dumbledore" ahead.

Dumbledore and Grindelwald took a blood oath to not fight each other

"Fantastic Beasts: The Crimes of Grindelwald," the second film in the series, reveals that as teenagers Dumbledore and Grindelwald undertook a blood pact that wouldn't allow them to move against each other. It was the biggest obstacle in the way of the duel between the two that we know, from past "Potter" lore, to eventually occur in 1945.

At the end of the second film, Newt delivers the pendant containing Dumbledore's and Grindelwald's drops of blood to Dumbledore, correctly guessing that it's a blood pact. Dumbledore says that he may be able to destroy it, but it's unclear.

Dumbledore struggles with the blood pact throughout 'The Secrets of Dumbledore'

The consequences of violating the blood pact were unclear in the second film. However, in an exchange at the Hog's Head, Aberforth Dumbledore's pub, at the beginning of "The Secrets of Dumbledore," Albus briefly demonstrates for Newt and Theseus what would happen if he attempted to move against Grindelwald.

The chain attached to the pendant begins to constrict around his skin, and the pendant itself becomes agitated.

Dumbledore warns that there could be consequences even if the pact sensed a betrayal in his heart.

The pact eventually breaks in a recreation of an old three-way duel

In Bhutan, Grindelwald moves to attack Credence (who's really Aurelius, Aberforth's son) after he betrays the dark wizard, revealing to those present that the qilin that chose Grindelwald was in fact a charmed corpse. Aberforth and Albus both move to protect Credence/Aurelius, effectively recreating the long-ago duel that left Albus and Aberforth's sister Ariana dead.

Somehow, this three-way conflict breaks the blood pact. Even Albus isn't certain why, but it could have something to do with Grindelwald's desire to harm Credence conflicting with Albus' desire to protect him.

With the pact broken, Grindelwald and Albus engage in a brief duel that appears to take place in a separate, isolated dimension. It ends in a stalemate, and Grindelwald escapes consequences once again and flees Bhutan.

The pact being broken finally means the door is open for Dumbledore to eventually defeat Grindelwald in 1945. In his obituary for The Daily Prophet, which appears in the second chapter of "Harry Potter and the Deathly Hallows," Dumbledore's friend Elphias Doge wrote that "no Wizarding duel ever matched that between Dumbledore and Grindelwald in 1945."

If the franchise continues, perhaps that duel is something we'll see in a future "Fantastic Beasts" film.