Author J.K. Rowling brings another revelation that is stirring up fans all over the world.

During a Q&A held on Twitter, the author surprised fans by spilling an important detail about Rubeus Hagrid, the Hogwarts groundskeeper and professor of a Magical Creatures subject.

"Hagrid couldn't produce a Patronus. It's a very difficult spell," answered Rowling on Twitter when asked what Hagrid's Patronus is.

A Patronus is a guardian in the shape of an animal that best represents the witch or wizard conjuring it. It appears when the Patronus charm, which can only be used by a wizard with proper skills, is cast.

Many fans have been surprised to hear this revelation. Although Rowling hints that his inability is related to Hagrid's incomplete education and difficulty in casting spells, fans are worried about another thing.

A Patronus charm only works by thinking of a happy memory. People like Harry Potter and Hagrid, who grew up with families that are not complete, are more likely to find it difficult to conjure a spell from a happy memory.

Fans are worried that Hagrid may not only be lacking the skills. It is also possible that he does not have any happy memory to conjure the Patronus from.

Harry Potter first learned how to cast the Patronus charm in the third book, "Harry Potter and the Prisoner of Azkaban." He used it to fight the presence of Dementors, black ghost-like figures that suck the life out of people. He also used the Patronus charm to save the life of his godfather, Sirius Black.

His full, corporeal Patronus takes the figure of a stag, just like his father's. Hermione Granger's Patronus is an otter, and Ronald Weasley's Patronus is a Jack Russell Terrier.

Many fans are still curious about what animal Hagrid's Patronus would be if he could conjure one. After all, the half-giant is known for his love for animals, particularly for dangerous beasts like giant spiders and baby dragons.

This August, the "Harry Potter" spin-off film titled "Fantastic Beasts and Where to Find Them," reports Entertainment Weekly. The book of the same title, written by J.K. Rowling, is a textbook recommended in Hogwarts' curriculum. In the Wizarding World, the book was written by Newt Scamander.

The film is going to explore the adventure of Newt Scamander, a magizoologist (a person who studies magical creatures), to be played by Oscar-winning actor Eddie Redmayne.

According to another report from Entertainment Weekly, the cast reportedly includes Colin Farrell, Dan Fogler, Ezra Miller, Samantha Morton, Jenn Murray and Faith Wood-Blagrove. The film is set to hit theaters on Nov. 18, 2016.