Firth played Elizabeth II's father, George VI in the Tom Hooper-directed feature about the WWII-era king who ascended the throne after his more dashing older brother abdicated in order to marry American divorcee Wallis Simpson in a scandal that rocked the British Empire even as the clouds of war gathered in Europe. Also starring Helena Bonham Carter as his wife, Elizabeth, the film focused on the shy George VI, known to relatives and close friends as Bertie, who overcame a severe speech impediment to help lead his country to face the Nazi threat.
The Press Association U.K. said that the new film is in the "very early stages," but Bonham Carter and fellow King's Speech co-star Geoffrey Rush are also likely to return. In this follow-up, Firth will return as George VI during the dark days of the Blitz, in which Buckingham Palace along with much of London during frequent night raids. Along with a Best Actor win for Firth, The King's Speech won Best Picture, Best Director and Best Original Screenplay.
Mirren, meanwhile, will take on the role of George VI's heir, Queen Elizabeth II in a new stage play written by The Queen author Peter Morgan, according to The Guardian. Stephen Daldry will direct The Audience, which will explore her confidential meetings with her long line of British Prime Ministers from her first as a young Queen, Winston Churchill, to the current office holder, David Cameron.
In The Queen, she meets with '90s-era P.M. Tony Blair (played by Michael Sheen) around the time of the death of Diana, Princess of Wales capturing a period of great tumult for the British royal family.
Appearing on Saturday Night Live shortly after her first stint playing Elizabeth II, Mirren famously said, "I'd like to say something for the record, although I played the Queen I am nothing like her. I may have been appointed Dame of the British Empire, but I am not all scones and teacups, I'm more biscuits and D-cups."
[Sources: The Press Association, The Guardian]