To be fair, it isn’t exactly a true spin-off per se. This is because according to Netflix, the new series will be based on the character Richter Belmont, who Netflix has described as being the great, great, great, great, and so on grandson of Trevor Belmont and Sypha Belnades, meaning that while it will focus on a new story, it will somehow be linked to the previous series, but set much later given how far down the family tree they are from each other.
— Netflix Geeked (@NetflixGeeked) June 11, 2021
This is similar to the game where Richter is described as being a somewhat very distant relative to Trevor. In addition to Richter, the announcement also confirms another character from the Castlevania video game series in the form of Maria Renard. The series will be taking place in 1792 during the French Revolution.
At the moment, there is no word on when the series will be released so until we get an official confirmation of the release date, don’t hold your breath just yet.