In a new story titled The Potter Family, the 51-year-old author reveals that Harry Potter's great-grandfather's name was Henry, but was called Harry by his close friends.
"Henry Potter (Harry to his intimates) was a direct descendant of Hardwin and Iolanthe, and served on the Wizengamot from 1913 – 1921," reads the post. "Henry caused a minor stir when he publicly condemned then Minister for Magic, Archer Evermonde, who had forbidden the magical community to help Muggles waging the First World War. His outspokenness on the behalf of the Muggle community was also a strong contributing factor in the family’s exclusion from the ‘Sacred Twenty-Eight."
The Sacred Twenty-Eight were families in the 1930's who were considered pure-blood, which the Potters are not.
The elder Harry was father to Fleamont Potter, who had James Potter, Harry's dad. According to Rowling, Fleamont and his wife, Euphemia, "lived long enough to see James marry a Muggle-born girl called Lily Evans, but not to meet their grandson, Harry."
Daniel Radcliffe went on to play the spectacled Boy Who Lived in eight of the Harry Potter films. ET spoke with Emma Watson, who played Hermione Granger in the franchise, during the premiere of Beauty and the Beast, where the Hogwarts alum shared that she and her former co-stars have a group chat.
Watch the video below for more on how Watson stays in touch with her Harry Potter pals.