"The Crown," a historical drama on Netflix, made a significant decision to replace the entire cast once the show moved into its third season. This decision was not based on performance or any internal disagreements, but rather was part of the original plan set out by the creator, Peter Morgan. The central reason for this is to accurately depict the aging of the characters as the series progresses through time. The show covers several decades of Queen Elizabeth II's reign, meaning that the characters must age realistically. Instead of using makeup and special effects to artificially age the original cast, Morgan decided it would be more believable to recast the roles with older actors. This method of casting acknowledges the authenticity of age and ensures that character portrayal remains realistic during the show's progression through time. So in the third season (which covers the years 1964-1977), older actors were cast to better represent the life stages of the characters. While this strategic change was quite abrupt, and no doubt disappointing for those who became attached to the cast from the first two seasons, it was a necessary and planned modification for the representation of the characters' journey through time. For the same reason, the cast changes again in season 5. In conclusion, the cast change in "The Crown" was a calculated decision to ensure realistic and authentic representation of the aging characters that the series portrays.