The story of Fantastic Beasts: The Secrets of Dumbledore looks set to payoff a key and intriguing line from Harry Potter and the Deathly Hallows. The backstory of Albus Dumbledore was partially covered in the Harry Potter books and movies, which explained his past relationship with the dark wizard Gellert Grindelwald, and made mention of the tragic death of his sister, Ariana. In both cases, though, there's much more to be explored, and other possible secrets as well.
That's something the Fantastic Beasts franchise is now diving into, with Fantastic Beasts 3 titled "The Secrets of Dumbledore." This comes after the introduction of the younger version of the character, played by Jude Law, in Fantastic Beasts: The Crimes of Grindelwald, and will presumably focus mostly on the biggest secret of them all, which was revealed at the end of that movie: Dumbledore's secret brother, Aurelius, previously known to viewers as Credence Barebone.
The plot twist, combined with the title of Fantastic Beasts 3, makes it clear that the history of Albus and indeed his entire family will be under much greater scrutiny in the upcoming Wizarding World movie. Exactly what will be revealed remains to be seen, but the fact that is so much secrecy surrounding his past life and so many shocking truths ready to come is something that was setup in Harry Potter and the Deathly Hallows. There, Aberforth tells Harry and co: "I knew my brother, Potter. He learned secrecy at our mother's knee. Secrets and lies, that's how we grew up." In the Deathly Hallows itself, that is largely taken as reference to the fate of Ariana, who was killed in a three-way fight between Albus, Aberforth, and Grindelwald, though the exact circumstances have not yet been uncovered, but Fantastic Beasts: The Secrets of Dumbledore could add much greater meaning to it.
The title alone - specifically, that it is Secrets, plural - means that there will be more to Dumbledore's story than the not-so-insignificant matter of his surprise brother. That itself, though, adds new context to Aberforth's Deathly Hallows quote, as it could perhaps be inferred that they both knew about Aurelius and had to keep it a secret for the sake of their mother, Kendra. It also suggests that Fantastic Beasts 3 could dive further into the past, and show just what happened to Ariana. Given Albus himself believes the killing blow may have come from his wand, then there's a chance to show the most devastating secret of his life, adding even greater weight to what Aberforth warned Harry about. Besides those two secrets, then there could be even further reveals to come about the Dumbledore family, given the Fantastic Beasts franchise is very much in the business of adding new layers to the lore of Harry Potter, even if it creates plot holes in the process.
There's also Dumbledore's other secret, which is his love for Grindelwald. The movies have never explicitly explored the fact that Dumbledore was gay, nor that he was in love with his old friend turned great rival, but it's something that Fantastic Beasts 3 will find hard to ignore. Just as Albus himself cannot keep on sending others to fight this war for him and hiding away from confronting Grindelwald, nor can the series continue to shy away from the truth of who these characters are and what they feel for one another. Whether Aberforth himself knew of Albus' feelings for Grindelwald is unclear, but he certainly knew that the Hogwarts headmaster kept a lot of secrets, perhaps more than anyone realized.
