Assumptions about Credence’s identity (COG spoilers..)
Grindelwald wasn’t lying, but he wasn’t telling the whole truth, either. Let’s look at things objectively.
Ezra Miller has now spoken about the ‘fact’ that Credence Barebone is Dumbledore’s brother / Aurelius Dumbledore.
First, in this IGN video he shares the story of how producer David Heyman told him (about two years ago) “You’re Dumbledore’s brother.” He thinks he is talking about Aberforth and apparently Heyman thinks so, too. Ezra is in shock, of course: “How do I get an English accent? How do my eyes turn blue?” like the good fanboy he is.
Then, a few weeks later, he meets Rowling and she tells him: “Oh, no. You’re not Aberforth, you’re Aurelius.” - “”Who’s that?” - “Nobody knows about him but me, Darling. And you now.”
Also, let’s look at this EW article: “Going into the second film, he says the knowledge that he’s a Dumbledore (yes, it’s apparently true) caused him to tweak his performance slightly.’Yes, on a certain, a very, very subtle level,’ Miller says. [...] ‘So as he changes, there’s an opportunity for me as an actor to look to five of my favorite performances of all time — the people I’ve seen play Albus and Aberforth. Shout out to all those incredible actors, and I’m thrilled to play the game that we’re now blood relations.’”
What does this mean? Firstly, I don’t think JKR is feeding Ezra Miller false information. Or that he is doing that to the public right now. It remains possible. But let’s assume they’re both saying the truth.
1) His real name Aurelius (as stated by Rowling according to Miller)
2) He is a Dumbledore, blood relative to Aberforth and Albus (as strongly indicated by Miller in the article)
3) He is Albus Dumbledore’s brother according to D. Heyman, BUT:
apparently that guy doesn’t know shit, thinking Credence was Aberforth
Rowling said Miller and herself were the only two people in the world who knew at that point
Rowling was probably only telling Heyman the ending to Crimes of Grindelwald (= what everybody knows now) and not the whole story which is set to be told over the the course of the next installments
It still wouldn’t be possible timeline-wise
So. This was exactly the way I’ve been thinking all along. Grindelwald wasn’t lying, but he wasn’t telling the whole truth either. Credence is a Dumbledore, but not a brother to Albus.
We know now that Credence was born in 1901 or 1900 (according to the screenplay’s date of the shipwreck). He might have received Ariana’s obscurus shortly after she died. But the question remains, where did the child itself come from?
I know some people think he might be the child of Honoria Dumbledore, the unmarried aunt who broke up with her fiancé because he had a kink of fondling some pink, fungus-like magical creatures (Horklumps), as explained in Dumbledore’s footnotes to The Tales of Beedle the Bard. Somehow... no. Just no.
And Ariana & Aberforth were too young and had a whole load of other problems at the time (plus it would make for cheap storytelling).
My best bet remains that Credence is the biological child of Albus Dumbledore and Gellert Grindelwald. Read here why.