The Crown," according to the Evening Standard.
The role is currently played by The Night Manager" Golden Globe winner Olivia Colman.
The British paper reports that the deal is "all but confirmed" for Bonham Carter play the sister of Queen Elizabeth II in the hit Netflix series. She was reportedly approached to play the older Elizabeth, but opted instead to play the "friskier" sister.
She previously played the future Queen Mother (and wife of King George VI) in "The King's Speech," for which she earned her second Oscar nomination. Coincidentally, Colman played the same role in "Hyde Park on Hudson." If you're a British actress, it's a given you're going to play a Queen at least once in your career.
No word yet on who'll take over as the older Prince Philip, who's currently played by former Doctor Who Matt Smith.
[Via Evening Standard]