"She was, of course, wonderful": The White Lotus star Carrie Coon opens up about her The Gilded Age Season 3 costar playing Bertha’s Sister

The Gilded Age Season 3 is broadening out its narratives with new family dynamics, and one of the big casting announcements has been spotted by viewers who have been keeping up for the long haul.

Carrie Coon, who plays the socially ambitious Bertha Russell, made the announcement recently that actress Merritt Wever has joined the cast as Bertha's sister. It was during the Monte-Carlo Television Festival in July 2025 that she announced the news while speaking with Deadline regarding season seven and how great it felt to be back working with Wever on screen.

Without giving away too much of the tale, Coon did say that Wever would appear as the sister of her character, and quipped:

"She was, of course, wonderful."

According to Deadline, she said,

"[Merritt] just walks in and she’s a person, and it puts everybody, I feel a little bit of shame when she’s acting, because I feel, suddenly, like you could see my acting from space when she’s there, but she was, of course, wonderful"

She added,

"And also, there’s a real learning curve when you come into the set, because the world has some size to it, and you have to figure out just what the camera can withstand, and when you’re kind of shrinking away from it and not being vivid enough for the world that you’re in."

Both women have fans who might recall their previous work on Fargo Season 3. Their re-emergence in The Gilded Age implies a shift in the story that will explore Bertha Russell's life beyond her professional ambitions among New York's upper echelons.

Carrie Coon confirms Merritt Wever's casting as Bertha's sister in The Gilded Age Season 3

The casting news comes as one of the strongest additions to the program. Coon shared her enthusiasm about the casting, explaining that she had long hoped to bring Wever into the series.

According to Deadline, Coon said,

"She was very self deprecating, and she was beautiful in the part, but she was kind of walking that journey with us, and I loved hearing her express it. But of course, we have all kinds of people guesting this year that are just marvelous, and everybody from the from the theater community that’s been able to join us has been such a treat"

This nod implies that Bertha's sister character will have a strong role to play in Season 3 and not merely as a background player. While HBO hasn't unveiled a complete character description, it is revealed that Wever's character, Monica O'Brien, is Bertha's estranged sister. Bertha's extended family will, for the first time, be probed by the show, and the introduction of a sibling can open up fresh social and emotional channels for an actress whose life thus far has been built on ambition, image, and wealth.

New dynamics in the Russell home in The Gilded Age Season 3

Bertha Russell has thus far been shown as an independently self-made woman attempting to carve out space for herself and her family in New York's upper echelons. The introduction of a sister, Monica O'Brien, could provide a glimpse into Bertha's earlier existence, perhaps before her ascension with George Russell.

Her introduction has the potential to energize unremediated complications, perhaps even undermining Bertha's well-built facade. Whether Monica helps or derails Bertha's highly planned family is uncertain, but emotional depth is an eventual dividend. The new family relationship can also have consequences for Bertha's children, Gladys and Larry, if Monica embodies values or experiences alien to their present mode of being.

Wever's track record

Wever's The Gilded Age casting follows the program's history of employing solid ensemble performers. Wever, whose understated, emotionally nuanced approach to acting, appeared in Unbelievable, Nurse Jackie, Godless, and The White Lotus. She is Emmy- and Golden Globe-nominated and has appeared in period dramas that have added richness to ensemble tale-telling throughout.

In a show so dependent on class war, reinvention, and generation war, Wever's Monica must be an opposition to Bertha's ideology. Whether she is set up as an enemy, a friend, or otherwise remains to be seen.

Filming and production timeline of The Gilded Age Season 3

Though HBO has not yet confirmed a premiere date for The Gilded Age Season 3, hints are already being dropped that production on the series is already happening.

Making comments in the same interview, Coon stated she had just returned from Thailand, where she was filming The White Lotus, and immediately began filming The Gilded Age, suggesting that filming on the show has already started. According to the release history of the series till now, Season 3 would likely release in late 2025 or early 2026.

Along with Wever, HBO also previously revealed the casting of financier J.P. Morgan, played by Bill Camp. There will be other new characters and real-life historical figures as well, which promises that Season 3 will not only continue to flesh out Bertha's life beyond the work for which she is known but will also have the series continue to cover late 19th-century American industry and finance.

The Gilded Age Season 3: What's been revealed so far

The Gilded Age Season 2 concluded with some of the characters at junctures, socially, politically, and emotionally. With the old money cliques of the city still fighting it out with newcomers such as the Russells, Monica O'Brien's introduction could be used to explore Bertha's journey from humble beginnings to what she is today in high society. HBO has not revealed episode titles, teaser promos, or official plot synopses so far, but the introduction of Monica's character already hints at tension within.

Thanks to Julian Fellowes' modus operandi, Monica's entrance is not likely to be accidental. The Downton Abbey alum also tends to introduce characters who upset the apple cart. In Monica's instance, she can be representative of Bertha's history in a world Bertha no longer wants to accept, or still lives within on an emotional level.

Until the teasers arrive officially, much of the plot in Season 3 is a rumor. But news that Merritt Wever is going to play Bertha's sister is more than a casting afterthought. It is a significant move toward the emotional escalation of a show that, thus far, has been concerned with external ambition and class aspiration. If Monica introduces family secrets or opposite values, the air inside the Russell home might shift profoundly.

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Will she help bring Bertha to power, or remind her of what she once was? Only time (and HBO) will reveal.

Also read: "Please renew it already": Fans cannot get enough of The Gilded Age as HBO drops mid-season trailer for Season 3

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