The Harry Potter fan theory that solves one of the series' biggest mysteries.

Two and a half weeks after the release of Fantastic Beasts and Where to Find Them, fans have blown wide open a theory about two important characters from the wizarding world.

In a post on Reddit, user Janu567 reveals a possible reason as to why Hogwarts headmaster Albus Dumbledore’s sister, Ariana, is rarely talked about in the Harry Potter series.

And it’s because, according to Janu567 at least, Ariana was an obscurial.

Image via Warner Bros. 

Like Credence in Fantastic Beasts and Where to Find Them, an obscurial is a magical parasite that develops when a wizard or witch doesn't use their powers or tries to hide their true self from those around them. But the more a witch or wizard tries to suppress their magical ability, the more likely their magic is to destroy them.

As readers of J.K Rowling's best-selling books will remember, Ariana Dumbledore's death was caused by a fight with her mother.

But despite being the sister of one of the world's greatest wizards, her presence isn't known until Harry Potter and the Deathly Hallows - the final installation in the seven-part series. And even then, she is only mentioned twice - once in an obituary, and then again at the end of the series when Harry meets Aberforth, Dumbledore's brother.

"She wouldn't do magic, but she couldn't get rid of it; it turned inward and drove her mad, it exploded out of her when she couldn't control it..." Aberforth told Harry in the movie.

And so enters janu567's theory, which goes like this: after an incident involving muggles, Ariana tried to bury her magical ability. But instead, her power turned inward and she would explode just like Credence does.

Image via Warner Bros.

The theory goes on to suggest that she got so angry that she could no longer control herself and released her full power, ultimately killing herself and her mother in the incident.

The theory also addresses the involvement of Grindelwald - the evil wizard seen leading Credence astray in Fantastic Beasts.

Originally learning about obscurials through his friendship with Dumbledore, Grindelwald becomes interested in their destructive powers and travels to New York to track down Credence and utilise his powers for bad.

Image via Warner Bros.

Fans agree that the captivating theory is likely true.

Faithfullyfanciful says on the Reddit thread, "Great theory, sounds very possible to me."

Another says "Yup. The way Aberforth describes it, it definitely sounds like an obscurial."

Whether you believe this or not it definitely fits in with what an obscurist is meant to be.

Let's hope that the sequels of Fantastic Beasts and Where to Find Them shed more light on whether or not this is true.