She'll be joining the likes of Elle Fanning, who plays future Russian empress Catherine the Great and Nicholas Hoult, who stars opposite as her temperamental husband, Peter in the deliciously dark historical drama.
The actress, whose recent turn as Margaret Thatcher in The Crown won her a Golden Globe, will be taking on the role of Joanna, Catherine's mother. Find out more below...
WATCH: Have you watched season one of The Great?
The 52-year-old actress will appear in two episodes of the upcoming season and has been described as a glamorous German socialite who's known for her match-making skills, having arranged high-profile partnerships for all her daughters.
As per Deadline: "[Joanna] has heard rumours of her daughter's coup and come to Russia to see it for herself. Though the apple of Catherine's eye and a doting mother, it soon becomes clear Joanna has more sinister intentions to save her family's reputation."
The satirical series, created and written by Tony McNamara, co-writer of the BAFTA-winning The Favourite, charts the rise of Catherine the Great from young bride and outsider to Russia's longest-reigning female monarch.
The Great season two is filming now
Season one premiered on Hulu in May 2020 for US audiences and landed on Channel 4 in the UK at the beginning of this year. While there's no update on when season two will arrive, news of Gillian's casting combined with a first-look photo of Elle back in costume which was released back in February, suggests that production is well underway.
Critics and viewers alike had high praise for season one, with many taking to Twitter to share their thoughts. One person wrote: "#TheGreat is truly just that. It's smart, funny, incredibly well acted, and just great fun".
Another added: "Loved The Great. Channelling The Favourite superbly. If you're going to do a historical drama loosely based on fact, you'll may as well just go for it. Elle Fanning and Nicolas Hoult are sensational." A third person tweeted: "I'm not only getting The Favourite vibes from this, but also a feeling this will be my new must-see TV. Loving this already!"
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