'Fantastic Beasts: The Secrets of Dumbledore' makes an unexpected reveal about a famous wizarding family. Here's what to know.

• Warning: Major spoilers for "Fantastic Beasts: The Secrets of Dumbledore" below.
• "Fantastic Beasts: The Crimes of Grindelwald" made a major reveal about a wizarding family.

The title of "Fantastic Beasts: The Secrets of Dumbledore" makes some big promises about unraveling one of the most mysterious wizarding families depicted in the "Harry Potter" series.

Not only does it feature the return of Jude Law as Albus Dumbledore, it also features Albus' brother Aberforth (Richard Coyle). The character was last seen as a much older man in "Harry Potter and the Deathly Hallows: Part 2," played in that film by Ciarán Hinds.

There were plenty of unanswered questions about the Dumbledore family at the end of the previous "Fantastic Beasts" film, "The Crimes of Grindelwald." After Grindelwald told Credence Barebone that he was Aurelius Dumbledore, the brother of Albus Dumbledore, fans were left confused as a result of the sudden reveal.

"The Secrets of Dumbledore" clears up that confusion in yet another shocking reveal.

Warning: Major spoilers ahead for "Fantastic Beasts: The Secrets of Dumbledore."

The end of 'The Crimes of Grindelwald' blew open the Dumbledore family's history

At the end of "The Crimes of Grindelwald," Grindelwald tells Credence that his name is actually Aurelius Dumbledore, and that his brother — presumably referring to Albus – is trying destroy him.

The reveal left fans puzzled, mostly because timeline-wise, it wasn't possible for Albus and Aurelius to be brothers. Percival Dumbledore, Albus and Aberforth's father, was imprisoned before Albus entered Hogwarts in 1892. Their mother, Kendra, died in 1899.

However, Ezra Miller, who plays Credence in the films, stated that the character was 18 years old in the first "Fantastic Beasts," which is set in 1926. That would place his birth somewhere around 1907 or 1908, and it would have been impossible for him to have been born to either of the Dumbledore parents.

There was some speculation at the time that Credence could have been tied to Albus and Aberforth's aunt, Honoria, who is first mentioned in the spin-off book "The Tales of Beedle the Bard." However, little was known about her.

It turns out that Credence isn't Albus' brother — he's his nephew

"The Secrets of Dumbledore" circumvents the timeline issues by revealing that Credence — or rather, Aurelius — isn't Albus' brother. He's Aberforth's son, which makes him Albus' nephew.

Albus explains to Newt in a conversation at Aberforth's pub that the same summer he and Grindelwald fell in love, Aberforth also had a relationship with a girl who also lived in Godric's Hollow. The girl, Albus says, was eventually sent away amid rumors of a child.

While Albus was unaware of the child, he said that the boy would have been a part of their lives had he known.

Furthermore, he confirms a long-held theory that his sister Ariana, who died during a three-way duel between Albus, Aberforth, and Grindelwald, was an Obscurial like Credence.

Aberforth and Credence reunite at the end of the film

Aberforth travels to Bhutan with the rest of the crew in pursuit of Grindelwald, and for the International Confederation of Wizards convention.

When he's there, he's able to finally reunite with Credence/Aurelius, who betrays Grindelwald by telling those assembled that the qilin that chose him was, in fact, dead, and had been charmed by the dark wizard.

The two also have a brief exchange that hearkens back to one of the most oft-quoted lines in the entire "Harry Potter" franchise. When Aurelius asks if Aberforth ever thought of him, Aberforth replies, "Always."

The line was originally said by Severus Snape in the series' eighth and final film. When Dumbledore asks him if, after all this time, he's still in love with Harry's mother Lily, he replies, "Always."