The 38-year-old won the heart of Lady Mary as Henry Talbot in ITV's period drama favourite and now he's set for the role of Antony Armstrong-Jones, AKA Lord Snowden, who was Princess Margaret's husband from 1960 to 1978.
The show's creator, Peter Morgan, revealed at the beginning of the month that the next season would see some new faces introduced, including that of Lord Snowdon.
Morgan told People that it will focus more on Prince Philip and Prince Charles, as well as seeing Princess Margeret finding love again with the Bourgeois photographer who she will go on to have two children with.
Matthew will join the Golden Globe-winning show to play Lord Snowdon opposite Vanessa Kirby's Princess Margaret.
Downton star Matthew will play Princess Margaret's husband in The Crown season 2
Season two of Netflix's hit royal drama will introduce a few new faces
The cast of The Crown vs the real Royal Family
Thu, December 22, 2016
Netflix's The Crown and the Royal Family: How much do the actors; Claire Foy, Matt Smith & Vanessa Kirby look like the real Royal Family.
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Claire Foy as Queen Elizabeth II
The real-life relationship between Lord Snowdon and Princess Margaret was fraught, with a drawn out and public breakdown of their marriage.
He died peacefully at home on January 13 at the age of 86.
Season one covered Queen Elizabeth II's life from 1947 to 1955 and ended with her marriage at breaking point as Prince Philip struggled to adjust to her new role as Queen.
The real-life Princess Margaret and Lord Snowdon were married for 18 years and had two children
Matthew will play opposite Vanessa Kirby in her role as Princess Margaret in The Crown
Season two will pick up roughly where the first season finished and cover the events from the 1956 Suez Crisis through to the mid-1960s.
Actress Claire Foy, 32, who plays the Queen recently opened up about how the show will undergo a total cast overhaul after the second season.
Producers plan to make six seasons spanning the whole of the Queen's life.
Seasons three and four will see the whole current cast replaced, and five and six will see yet another change as the actors are succeeded by an older cast to play the royals in most recent stage of their lives.