The bigger surprise is Tobias Menzies (Outlander, Game of Thrones), who takes the role of Prince Philip, previously played by Matt Smith, just as the royal husband's story gets a bit deeper and darker.
Philip's midlife crisis — triggered in part by his envy of the American astronauts who land on the Moon — is a study in the fragility of male ego.
He is also jangled by the sudden presence of his elderly mother, an orthodox nun (scene-stealer Jane Lapotaire) once known as Princess Alice of Battenberg, who found solace from mental illness and emotional demons by devoting her life to charity. After a military coup in Greece, the palace brings an ailing Alice to stay, over Philip's objections. He warms to her once he sees the press adores her, dubbing her "the Royal Saint".
Public perception becomes a preoccupation for the Windsors.
A day-in-the-royal-life BBC doco, meant to humanise the family, is generally regarded as a dud, especially by the Queen herself.
It's Princess Margaret, her increasingly dissatisfied sister (now played by Helena Bonham Carter), who possesses the true gift for limelight. On a US trip, Margaret scores big with the glitterati in San Francisco and LA.
Her celebrity, though greeted with quiet disapproval in the palace, is also seen as an asset — so much so that Margaret is diverted to Washington to charm President Lyndon Johnson (Clancy Brown), who has taken a chillier view of US-Britain relations than JFK did.
The Queen, meanwhile, has one of her earliest reckonings with class and suffering in the modern era, as she wrestles with an appropriate response to the deaths of 144 people, mostly children, in the 1966 Aberfan, Wales, disaster.
It's a foreshadowing, of sorts, of the delayed royal tears after Princess Diana's death decades later, depicted memorably in Morgan's screenplay for the 2006 film The Queen.
The third season of The Crown is screening now on Netflix.