Funnily, both actors have previous playing the same royal - the Queen Mum: Olivia Colman in Hyde Park on Hudson and Bonham Carter in The King's Speech.
However, the show will be making a time jump, so Netflix is recasting for storylines about the later years of the royal family's lives.
The second season of the drama series from Peter Morgan launched December 8 on the streamer.
"You can't ask someone to act middle-aged", Morgan told the outlet. She would be replacing Vanessa Kirby, who was sensational during her time on the show in the role. "The feelings we all have as 50-year-olds are different than the feelings we all have as 30-year-olds", Morgan explained.
Call for 'latte levy' to cut disposable coffee cup waste
A more focused target has thus been recommended: all single-use coffee cups placed in recycling bins to be recycled by 2023 . These were "well meaning", MPs said, but not enough to tackle the scale of cup waste in the UK.
According the the Evening Standard, Helena was rumoured to be eyeing up the role of Queen Liz herself but it seems she was far more suited to play the more risqué Windsor sister.
For Clare Foy, who is quite brilliant as the young "Her Majesty", it must feel like playing soppy Cinderella in a really high-class panto, while watching fellow actress Vanessa Kirby have all the Ugly Sister scenery-chewing fun. But it would be a ideal thrill to see her on The Crown-a sumptuous, thoughtful series that has brought a dazzling new appeal to the royal family. But as synonymous as Foy, Matt Smith, Kirby, and the others have become with their roles, they have worthy successors.
The third season will shift the story into the 1970s, and will include Princess Margaret and Lord Snowdon's 1976 separation and 1978 divorce.