Sorcerers, werewolves, vampires… And now the Fae. We already had hints of it from the previous books, particularly in the guise of Lea–Harry’s literal Fairy Godmother.
Overall, it’s a very cool bit of worldbuilding. The Fae aren’t particularly uncommon in Urban Fantasy and I really like the Dresden Files version thereof. They’ve even gotten to the point where they act as background knowledge when reading other series. If something isn’t mentioned, I’ll fall back to the Dresden Files as ground truth. It’s just that solid.