Aurelius Dumbledore Parents & Backstory
Although Grindelwald doesn't confirm who exactly Aurelius's parents are, since he refers to Albus as the young man's brother we can presume the two share one or both parents. Albus was the eldest son of Percival and Kendra Dumbledore, a wizard man and muggle-born woman. It was thought by the Wizarding community that there were only three Dumbledore children: Albus, Aberforth and Ariana. Ariana, of course, was likely an Obscurial, who died young (she's never confirmed to have had an Obscurus, but there are too many parallels between her and Credence/Aurelius to be ignored). Ariana died in the summer of 1899 during a three-way duel between Albus, Aberforth and Grindelwald.
As for Kendra and Percival, the latter was arrested by the Ministry of Magic in 1890 and sentenced to Azkaban for attacking a group of muggle boys who had tortured Ariana when she was six. He supposedly died in Azkaban sometime later. Kendra, meanwhile, died in early summer 1899, two months prior to Ariana. Kendra was killed by an uncontrolled fit had by Ariana (another clue the young girl was an Obscurus).
So, if Aurelius is a Dumbledore, it's unlikely he's the son of both Kendra and Percival. Since Percival was sentenced to Azkaban in 1890, and prisoners of Azkaban can only receive visits from members of the Ministry of Magic, it seems incredibly unlikely Kendra and Percival would have been able to conceive a child after 1890. However, if Kendra were to have conceived a child outside of wedlock with another man, and given birth to that child before her death in 1899, he would be Albus's half brother and technically a Dumbledore, but would explain why his birth was hidden from the Wizarding community. It would also explain why baby Aurelius was on a ship bound for America.
As revealed by Leta Lestrange (Zoë Kravitz), she switched her own baby brother Corvus with an unknown baby that grew up to be Credence/Aurelius. During Leta's story, it's unclear who the baby and the woman taking care of him are. However, the credits may be able to offer some insight. A character referred to as "Credence's aunt" is played by Linda Santiago. It's likely this woman is Honoria, the spinster aunt of Albus, which would also make her Credence/Aurelius's aunt. It's unknown whether Honoria is Percival or Kendra's sister, so it's unknown whether she's a muggle or a witch. But if Kendra had a baby out of wedlock and then died (or if Percival somehow managed to impregnate someone other than his wife while in Azkaban), it seems possible Honoria would flee with the baby to protect the Dumbledore name and/or Kendra's reputation.
All this is to say, it's not entirely clear who Aurelius's parents are, largely because so much about Dumbledore's family is unknown. And, since Credence was thought to be 18 in Fantastic Beasts and Where to Find Them, his age doesn't line up with what we know about Albus's parents. But again, powerful wizards age differently that muggles, so there's a way for Rowling and the Fantastic Beasts franchise to make it all work. But we'll need more information before knowing Aurelius's exact parentage and why he wasn't raised alongside the other Dumbledore siblings.
Aurelius Dumbledore Is New To Harry Potter Canon
Perhaps the most shocking aspect of the reveal about Credence's identity in The Crimes of Grindelwald is that it adds a new major character to Harry Potter canon. Although not much is known about Albus Dumbledore's family, Harry Potter and the Deathly Hallows offers the most information about the Boy Who Lived's mentor. It's in the time following Dumbledore's death that Harry learns about Albus's family - and when it's confirmed Albus only had two known siblings. But Rita Skeeter's The Life and Lies of Albus Dumbledore also makes it clear that there's a lot about the Dumbledore family the public doesn't know. Now it seems Rowling is introducing a new major member of the family in The Crimes of Grindelwald - though it remains to be seen how fans will take this new change to the Wizarding World canon or what it means for future Fantastic Beasts movies.
- Fantastic Beasts: The Crimes of Grindelwald/Fantastic Beasts 2 (2018) release date: Nov 16, 2018