Okay, so I've seen a lot of people watching Fantastic Beasts: The Crimes of Grindelwald and wondering whether Grindelwald is actually telling the truth and that Credence Barebone's true identity is Aurelius Dumbledore. I myself wondered this too until I sat down and did some Thinking 101 a couple of months ago.
If you're curious, read on.
*suspenseful silence*
Alright, let's get started. So, I'm going to say this kind of blatantly (huh I don't use that word often).
Credence cannot be the brother of Albus, Aberforth, and Ariana Dumbledore.
Why?
Well, we all know that Percival Dumbledore was convicted and that he died in Azkaban. He died sometime after 1890. Credence was born in 1901, so he couldn't have been born to Percival Dumbledore and some other woman.
Also, Kendra Dumbledore died in 1899, so she couldn't have given birth to Credence if she died two years before.
Credence cannot be the son of Albus Dumbledore.
If Dumbledore had a son, there would be at least one person on the planet that would know about it. Also, there is no mention of Dumbledore having a relationship with anyone. Except of course with Gellert Grindelwald. But they wouldn't have been able to have a child.
Credence cannot be the nephew of Albus Dumbledore.
There are some rumors that Credence is the son of Ariana Dumbledore. I don't mean to be rude to anyone who believes this, but I gotta say it: that is ridiculous. Ariana was trapped inside since she was seven years old. There was no possible way that she would have been able to go out without the watch of a family member. So, you know, she couldn't have - well - yeah.
Excuse me while I take a minute and barf.
Okay, I'm back.
Also, there is no record of Aberforth Dumbledore having a relationship, so he couldn't have had a son. Of course, I might be wrong - maybe he had a secret romance. I don't know. But he would have been 17 when Credence was born, so as much as him having a son at that age could be likely, I just don't think it happened. Again, I could be wrong.
There is the possibility that Honoria, the Dumbledore children's aunt, was Percival's sister, and maybe she never got married but still had a child. Or maybe Percival had some sort of long-lost sibling that no one knew about, and he/she had a child.
But what I'm saying is that there is no way possible that Credence could be the brother of the three Dumbledore children and it doesn't seem likely that he is a child of one of the Dumbledores.
Plus, Grindelwald is a villain - why wouldn't he lie to get what he wants?
And I'm going to say this one last time: I might be wrong. I mean, JKR is JKR. We don't know what goes through that crazy brain of hers.