Helena Bonham Carter to join The Crown as Princess Margaret

Helena Bonham Carter will be taking on the role of a middle-aged Princess Margaret in The Crown.

She's been the subject of speculation for months, since the makers of The Crown announced it was axing its entire cast for season three and replacing them with older actors.

The veteran actress, 51, will join Olivia Colman in the third and fourth seasons, as the pair play the royal sisters, the Daily Mail reports.

Helena takes the role from Vanessa Kirby, who has played the notoriously carefree princess in the Netflix show for its first two seasons. Colman is taking over from Claire Foy who has played Elizabeth II up until now.

The news was released on The Crown's official Twitter account on Thursday, along with the news that actors Jason Watkins will play Prime Minister Harold Wilson and Tobias Menzies will play Prince Philip.

Menzies takes over from Matt Smith's two-season portrayal as Prince Philip. Watkins will introduce Prime Minister Wilson for the first time, as John Lithgow portrayed the previous Prime Minister Winston Churchill in season two.

After former Princess Margaret actress Kirby was nominated for a TV Bafta for her portrayal of the Queen's younger sister, Bonham Carter has admitted that she's worried about filling the younger star's shoes.

"I'm not sure which I'm more terrified about - doing justice to the real Princess Margaret or following in the shoes of Vanessa Kirby's Princess Margaret," she said, as the news broke on Thursday. "The only thing I can guarantee is that I'll be shorter [than Kirby]."

The show's third run will not appear until next year, when it will stream on Netflix.