Meanwhile, Helena Bonham-Carter will be playing the queen's sister Princess Margaret, and Ben Daniels will be playing Margaret's husband, Antony Armstrong-Jones.
The plan is to have the period drama run for six seasons following the Queen's story throughout her whole life - each season representing a decade.
With the Royal Wedding and "Paddington 2" in the past, it's time to talk about another very British thing: "The Crown" season three.
On landing the role, Colman previously enthused: "I'm so thrilled to be part of The Crown".
The 44-year-old actress also quipped, "I'm basically going to rewatch her every episode and copy her!"
The actors join fellow actors Olivia Colman and Tobias Menzies. Thus, one discovers the actress of Broadchurch in full breakfast and the representative of a Queen already more assertive than during the first two seasons.
The third season of the show reportedly focuses on Prince Charles relationship with Camilla before he married Princess Diana and also Princess Margaret and Lord Snowdon's disintegrating relationship.
The sophomore season of the royal-family drama just received 13 Emmy nominations, including one for best drama.
Earlier this year, "The Crown" faced a gender pay gap controversy after it was revealed that Smith made more than Foy, even though she plays the character who wears the titular crown. Not to mention, the character of Camila Parker Bowles will start to play a role in the next season.
The new series is expected to land on the online streaming site in 2019.