WARNING! Contains SPOILERS for Fantastic Beasts: The Secrets of Dumbledore.
Fantastic Beasts: The Secrets of Dumbledore revealed Credence was really Aurelius Dumbledore, Aberforth'sestranged son, turning a hated plot twist into a good story. The third installment of the five-movie series saw Gellert Grindelwald (Mads Mikkelsen) rise to power and then fall once more as Dumbledore (Jude Law) and his team curb his ascension to Supreme Mugwump of the International Confederation of Wizards. The story is intertwined with several reveals about the Dumbledore family: Albus' relationship with Grindelwald, the story of Ariana, and of course, the reunion of Aberforth (Richard Coyle) and Aurelius/Credence (Ezra Miller).
When Johnny Depp's Grindelwald revealed Credence's identity as Aurelius Dumbledore in Fantastic Beasts: The Crimes of Grindelwald, the plot twist generated a predominantly negative reaction. Grindelwald claimed Aurelius was Albus' brother, but a fourth Dumbledore sibling was never mentioned before in the Harry Potter series. Furthermore, considering Kendra Dumbledore was dead and Percival was in Azkaban at the time of Credence's birth in 1900/1901, it created a big plot hole. However, if Fantastic Beasts' creators had retconned it by revealing Grindelwald had been lying about Credence's identity, the plot twist would have appeared as a cheap Warner Bros. trick for Fantastic Beasts 3, designed to attract more Dumbledore fans to the next movie. It seemed like the writers had dug themselves into a hole.
Instead, Fantastic Beasts 3 found a clean answer to the Credence/Aurelius twist, steering clear of huge plot holes or harmful retcons. Credence is the son Aberforth had with a woman from Godric's Hollow, but the woman was sent away and Aberforth never got to be a father. Albus expresses his regret for not being a better friend and brother to Aberforth: "He might have confided in me [...] This boy could have been part of our lives, part of our family." The Credence twist fits the Harry Potter canon, albeit reframing Aberforth's "secrets and lies" line from The Deathly Hallows. It seems like both Dumbledores have secrets, and Aurelius never being mentioned in Harry Potter adds to the fact that Aberforth wasn't necessarily right in criticizing Albus for his secrecy. Overall, the Credence/Aurelius twist made Fantastic Beasts 3 better, even giving deeper meaning to the film's title: it's not just a film about audience-favorite Albus, but a film about the whole Dumbledore family.
Through its Credence twist, Fantastic Beasts 3 also gave Aberforth a greater role to play - he had only made a proper appearance in The Deathly Hallows (played by Game of Thrones and Justice League actor Ciaran Hinds), and his conversation with Harry (Daniel Radcliffe) only brushed off his and Albus' past. Of course, while the film adds many layers to Aberforth's character, it also retcons a few things, such as Albus and Aberforth's relationship. Harry Potter canon states that Aberforth hated Albus for a long time, blaming him for Ariana's death (and even breaking his nose at her funeral). However, Fantastic Beasts 3 shows the brothers as having a fairly close relationship. Perhaps enough time has passed (over three decades) from Ariana's death for Aberforth to forgive and forget. Finally, Aurelius is never mentioned in the Harry Potter series, but this makes sense considering the Dumbledores' now-famous secrecy.
After the plot holes created by The Crimes of Grindelwald (Minerva McGonagall being at the forefront), it was good to see Fantastic Beasts: The Secrets of Dumbledore be more careful about its plot and revelations. Aurelius Dumbledore fits the canon and Fantastic Beasts 4 and 5 can develop his character, but the creators must tread lightly. If Aberforth and Credence becomes too big a story (and if Credence survives the fifth movie), the Harry Potter canon will definitely suffer a negative impact.