WARNING: The following article contains spoilers for Fantastic Beasts: The Crimes of Grindelwald, in theaters now.
Fantastic Beasts: The Crimes of Grindelwald sets up a lot of plot threads to be explored, but many of the film's major twists and turns center around the true identity of Ezra Miller's character, Credence Barebone, who survived his supposed death at the climax of 2016's Fantastic Beasts and Where to Find Them, spending time in a European circus before breaking free and searching Paris for his mother.
Similar to the first film, multiple parties are hunting Credence due to his repressed, magical potential, including the titular villain and mysterious French-African wizard Yusuf Kama. It is assumed by Credence and Yusuf that the character was originally born in Paris before being sent to America, with many hints that Credence is actually the long-lost half-brother Leta Lestrange and de facto stepbrother of Yusuf as the product of a marriage by Leta's father and his wife. This red herring is further supported by Credence visiting the midwife who attended his birth and accompanied him to America, before she's killed in the crossfire by a magical bounty hunter named Grimmson, who is trying to eliminate Credence once and for all.
Despite this set-up, the film's final scene gives us its biggest twist: Credence isn't a secret Lestrange at all, he's a secret Dumbledore. Grindelwald takes Credence under his wing in a remote Austrian castle and informs his new protege that he is, in actuality, a previously unknown younger brother to Albus named Aurelius. To further corroborate and seemingly confirm Grindelwald's shocking revelation, Credence summons a phoenix in the film's final moments, the mythical bird forever associated with the Dumbledore family to appear in times of the family's need.
Most of the clues to Credence's actual parentage and the film's final twist come from Dumbledore himself, if largely incidentally. It is Dumbledore who notes that the phoenix will arrive for family members in their moment of need, foreshadowing the bird's appearance in the final scene. And when Leta Lestrange has a conversation with her old professor, she asks him point blank if he had ever lost a brother. Dumbledore doesn't answer the question directly, instead citing the loss of a younger sister while alluding that her death was the cause of his acrimonious split from Grindelwald decades previously.