On Sunday night, July 13, 2025, The Gilded Age Season 3 reached a pivotal midpoint with an episode that centered on the much-anticipated wedding of Gladys Russell (Taissa Farmiga) to the Duke of Buckingham (Ben Lamb). But beyond the lavish nuptials, the episode marked a significant moment for fans of the HBO drama: the long-awaited introduction of Monica O’Brien, portrayed by Emmy-winning actress Merritt Wever. Monica is Bertha Russell’s (Carrie Coon) sister, a fact that had been hinted at since the show’s premiere but never fully explored—until now.
For two seasons, Monica was a shadowy presence, mentioned but unseen, while Bertha staunchly guarded the secret of her sister’s existence. George Russell (Morgan Spector), Bertha’s husband, had initially wanted Monica to join them in their grand mansion on 61st Street, but Bertha dismissed the idea, preferring to cultivate new friendships among New York’s established upper crust. However, the pressure from family, particularly from Bertha’s son Larry (Harry Richardson), eventually forced her hand. Larry extended the invitation to Monica for Gladys’s extravagant wedding, much to Bertha’s surprise and displeasure.
Monica’s arrival at the Russell mansion was a study in calm confidence, immediately highlighting the tension between the sisters. While Bertha’s cool reception was palpable, George and Larry welcomed Monica warmly, setting the stage for complex family dynamics. At a dinner scene that has already drawn praise, Monica did not shy away from asking pointed questions, challenging the carefully maintained facades of the Russell household. This interaction underscored the stark contrasts within the family, especially when Monica matter-of-factly declared she would wear the same dress to both the rehearsal dinner and the wedding itself—a choice that seemed to scandalize Bertha enough to orchestrate a coffee spill, perhaps to save face for their high-society guests.
Carrie Coon, who plays Bertha, has spoken candidly about the impact of Merritt Wever’s performance on set. In interviews with Deadline and Decider, Coon admitted to feeling a touch of professional envy at Wever’s effortless and deeply truthful portrayal of Monica. “Of course, Merritt, not only did she fit in seamlessly, but she also made me feel terrible because she’s just such a truthful and natural actor,” Coon shared. “When you see somebody like Merritt Wever walk on our set and just feel like a human being—which is something we fought so hard to feel like at the beginning—it just feels like, ‘I’m doing it wrong!’”
This humility and admiration highlight the collaborative spirit behind The Gilded Age, where new cast members like Wever inspire seasoned actors to elevate their craft. Coon noted a “learning curve” for actors joining the show, given the challenge of balancing the period drama’s grandeur with authentic, vivid performances. Wever herself described the acting “channel” on the show as “so narrow that you have to walk in the show because you can feel too theatrical, but you could also feel like you’re too small for the costume and the space.” Her ability to navigate this fine line has been widely praised by both cast and critics alike.
Wever brings a wealth of experience to the role of Monica, having won an Emmy for her work on the darkly comedic series Nurse Jackie and delivered acclaimed performances in diverse projects such as the Western Godless, the crime drama Unbelievable, the dark romantic comedy Run, and the Apple TV+ hit Severance. Her versatility and depth have clearly enriched The Gilded Age, adding new layers to the show’s intricate social tapestry.
Her chemistry with the cast, particularly with Carrie Coon and Morgan Spector, has been a highlight of the season. Spector revealed to Decider that his favorite moments with Wever involved shared inside jokes between George Russell and Monica, quietly exchanging looks that conveyed their mutual exasperation with Bertha’s domineering ways. “I feel like the history that we both got to bring that moment was like a history of kind of looking at Bertha and being, ‘Jesus Christ,’” Spector said, raising his eyebrows. Coon echoed the sentiment with a giggle: “There she goes again.” These subtle dynamics add dry humor and authenticity to the otherwise tense family scenes.
Monica’s debut has done more than just introduce a new character; it has reshaped key plotlines in Season 3. Her presence invites fresh scrutiny of Bertha’s calculated social ambitions and forces other characters to reassess their loyalties and alliances. Through Monica’s perspective, viewers gain a nuanced understanding of the Russell family’s internal conflicts and the broader societal pressures of 1880s New York.
Beyond Monica’s arrival, Episode 4 also introduced other notable characters, including Lady Sarah, the Duke’s sister, played by Hattie Morahan, and a psychic portrayed by Andrea Martin, whom a grieving Ada (Cynthia Nixon) visits in an effort to connect with her deceased husband. These additions, alongside the influx of talented guest actors from the theater community, have enriched the season’s ensemble, creating what Coon described as “an embarrassment of riches.”
As The Gilded Age continues to unfold, the integration of Monica O’Brien stands out as a masterstroke of storytelling and casting. Merritt Wever’s nuanced performance has not only expanded the show’s narrative depth but also invigorated the cast, raising the bar for the episodes to come. With Gladys’s wedding serving as a backdrop, the Russell family’s secrets and tensions simmer to the surface, promising a riveting continuation of this lavish period drama.
