season one in April of 2018, season two in May of 2018 and season three in February of 2020.
The fourth season spans 1977 to 1990. It is set during Margaret Thatcher's period as prime minister and also focuses on Lady Diana Spencer. Events depicted include Lord Mountbatten's funeral, the wedding of Prince Charles and Lady Diana Spencer, the births of Princes William and Harry, the Falklands War, Michael Fagan's break-in at Buckingham Palace, the Prince and Princess of Wales's 1983 tour of Australia and New Zealand, the Princess of Wales's appearance at the Barnardo's Champion Children Awards, and Thatcher's departure from office.
Olivia Colman stars as Elizabeth, along with main cast members Tobias Menzies [Prince Philip], Helena Bonham Carter [Princess Margret], Josh O'Connor [Prince Charles] and Erin Doherty [Princess Anne]. Season four adds Gillian Anderson as Margaret Thatcher and Emma Corrin as Diana, Princess of Wales.
Personally, I think that this may be the best season of The Crown so far. Gillian Anderson's performance as Margaret Thatcher is astonishing. The season paints Charles as a spoiled, petulant child; he is not a sympathetic character. I really enjoyed this season and highly recommend it.