"The X-Files" star won rave reviews and awards for her portrayal of Margaret Thatcher on Netflix's "The Crown", and now she's gearing up to join the cast of the Hulu comedy, starring Elle Fanning and Nicholas Hoult.
Gillian will play the socialite mother of Fanning's character Catherine the Great.
She will appear in two episodes of the second season.
James Mangold will direct the film after producer Steven Spielberg stepped down.
Production is expected to begin over the summer and the film is set to hit cinemas on 29 July 2022.
"Indiana Jones V" will be the follow-up to 2008's "Indiana Jones and the Kingdom of the Crystal Skull", which earned over $790.6 million (£568.7 million) at the global box office.
Director James Mangold recently said of the upcoming movie, "I'm thrilled to be starting a new adventure, collaborating with a dream team of all-time great filmmakers."
"Steven, Harrison, Kathy, Frank, and John are all artistic heroes of mine. When you add Phoebe, a dazzling actor, brilliant creative voice and the chemistry she will undoubtedly bring to our set, I can't help but feel as lucky as Indiana Jones himself."