The Crown Season 3 is already streaming on Netflix, but Netflix is already prepping the show’s fourth season.
Robert Lacey was interviewed on Virgin Radio on 3 December with Chris Evans and said:
What’s interesting about each Crown series is that it goes with a particular Prime Minister, we’ve just had Harold Wilson. Who came after Harold Wilson? Mrs Thatcher. And we already know that Gillian Anderson will be playing Margaret Thatcher – and that’s what we are filming at the moment.
Other details of The Crown Season 4:
https://www.harpersbazaar.com/culture/film-tv/a27101318/the-crown-season-4-news-date-cast-spoilers/