In the Harry Potter series, many of Voldemort's horcruxes were give rich backstories, like Tom Riddle's diary, Marvolo Gaunt's ring, and of course, Harry himself. But the most personal horcrux containing a fragment of Voldemort's soul is also the biggest mystery. Voldemort carries Nagini the snake with him wherever he goes, but we still don't know how the two met or where Nagini came from. Fans may not have to wait much longer to find out: One fan theory laid out by Vanity Fair suggests that Nagini is actually a cursed witch, and her true identity will be revealed in the next Fantastic Beasts movie.

On March 13, the trailer dropped for Fantastic Beasts: The Crimes of Grindelwald, the second installment in the Harry Potter prequel series written by J.K. Rowling. The clips include lots of goodies for fans—including a first look at Jude Law as young Dumbledore—but one potential bombshell requires closer examination.

Pay attention at the 1:07 mark in the video below and you'll see Claudia Kim, the actress playing a new, unnamed character in the film. While we don't know much about her yet, Pottermore tells us that she is a Maledictus or “someone who suffers from a ‘blood curse’ that turns them into a beast.” This revelation led some fans to suspect the beast she transforms into is Nagini, the snake destined to be Voldemort's companion.

That isn't the only clue backing up the theory. The second piece of evidence comes in the trailer at the 1:17 mark: There, you can see an advertisement for a "wizarding circus," featuring a poster of a woman resembling Kim constricted a by massive snake.

If Kim's character does turn out to be Nagini, the theory still doesn't explain how she eventually joins forces with Voldemort and becomes his horcrux. Fans will have to wait until the film's release on November 16, 2018 for answers. Fortunately, there are plenty of other Harry Potter fan theories to study up on in the meantime.

[h/t Vanity Fair]