This opens larger questions about Aurelius' parentage: Who exactly is the forgotten Dumbledore's father and why was the family on their way to America? It was revealed in The Deathly Hallows that Ariana had been assaulted by Muggles as a child after they witnessed her use magic, severely traumatizing the young Dumbledore. In retaliation, Ariana and Albus' father, Percival, killed the Muggle boys, resulting in his lifelong imprisonment in the magical prison of Azkaban, leaving their mother Kendra to care for them. In a traumatic episode, Ariana temporarily lost control of her powers and accidentally killed her mother, leaving her older brothers to care for her before her own untimely end.
This leaves the possibility that Percival fathered a fourth child during his imprisonment, with the still-unidentified mother moving to America for her own fresh start with her newborn son. Given Aurelius' considerably younger age than Albus, this makes more sense than him simply being Aberforth under a different name; previous text had listed Aberforth as only three years younger than Albus, who is visibly middle-aged by the events of The Crimes of Grindelwald, while Aurelius is still a much younger man. With much of this most recent film centered on Credence trying to discover the identity of his mother, a sequel would continue to explore this while navigating the Dumbledore family tree.
There is always the possibility that Aurelius isn't a half-brother to Albus at all, but rather a more distant relative, such as a cousin or nephew fathered by Aberforth -- but this is similarly unlikely. The personal and groundbreaking nature of Aurelius' identity would place him closer to Albus, with the possibility of him being a cousin undercutting the gravity of the reveal of him being a potential brother instead.
Written and co-produced by Rowling herself, the revelation of Credence Barebone as Aurelius Dumbledore is certainly within the Harry Potter creator's ultimate vision for her bestselling franchise rather than from an unaffiliated screenwriter. For a series of prequel spinoff films that explore the untold history of the Wizarding World decades before the birth of Harry Potter, the revelation of a previously unheard of Dumbledore family member is the biggest reveal for either prequel to date. Not only does it immediately up the personal ante at the heart of the prequels' central conflict, but it opens the door for far more scandalous revelations about Albus' past before he would become a mentor to Harry and headmaster of Hogwarts School of Witchcraft and Wizardry. With a further three films planned, audiences are about to see how far the rabbit hole of Albus Dumbledore's hidden history goes.
In theaters now, Fantastic Beasts: The Crimes of Grindelwald is directed by David Yates from a script by J.K. Rowling. Rowling. The film stars Eddie Redmayne, Jude Law, Johnny Depp, Katherine Waterston, Alison Sudol, Dan Fogler, Ezra Miller, Zoë Kravitz, Fiona Glascott and Callum Turner.