Eagle-eyed Harry Potter fans have spotted that in book six, the Half-Blood Prince, Professor Horace Slughorn refers to Ron Weasley as ‘Rupert’.
Page 454 of Bloomsbury’s 2005 edition of Harry Potter and the Half-Blood Prince
It seems highly unlikely that JK Rowling and her editors would have slipped up and muddled the character’s name with actor Rupert Grint who plays him in the films.
Instead, we reckon she was having some fun with Slughorn’s character traits and his penchant for focusing on the most talented students. Ron is no ‘Chosen One’ after all and getting his name wrong is simply another way to hammer home Slughorn’s disinterest in the Weasley boy. Making it a nod to Mr Grint appears to be a fan-friendly extra.