The Gilded Age Season 3 Episode 4 finally introduces us to a character we first heard about all the way back in the HBO show’s series premiere. At long last, Bertha Russell (Carrie Coon) is forced to invite her sister Monica O’Brien (Merritt Wever) to 61st Street. Hardcore Gilded Age fans will recall that George Russell (Morgan Spector) wanted to invite Monica to stay with them as soon as they settled into the massive mansion, but Bertha shrugged the suggestion off. She was more interested in making new friends among the upper crust of “old” New York. Now, though, she must cave to her own family’s pressure to invite Monica so she can attend Gladys’s (Taissa Farmiga) lavish wedding to the Duke of Buckingham (Ben Lamb).

Even though we’ve only just met Monica in The Gilded Age Season 3 Episode 4, she still feels like a fully fleshed out character and beloved member of the Russell family. That’s in huge part thanks to the work of Emmy-winning actress Merritt Wever. Her seemingly effortless arrival on The Gilded Age actually made Carrie Coon a tiny bit jealous.

“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,” Carrie Coon told DECIDER. “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!’ Like, that’s the feeling I had.”

After laughing about this, Coon explained that one of the best parts about welcoming “marvelous actors” like Merritt Wever onto the show is how the rest of the cast is “always learning” from them.

“Merritt describes, she said, ‘The channel is 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,’” Coon said. “And I thought that was a really good description. Like you just have to find that ‘channel.’”

Merritt Wever has a long career of figuring out exactly how to calibrate her talents for a variety of genres on TV. After winning the Emmy for her comic work in Nurse Jackie, she went on to deliver stunning performances in the Western Godless, the crime drama Unbelievable, dark rom-com Run, and the Apple TV+ hit Severance.

Morgan Spector revealed to DECIDER that his favorite part of working with Wever on The Gilded Age was finding a shared inside joke between George Russell and his sister-in-law.

“I also enjoyed how, you know, George and Monica only have like a couple of little moments together, but I feel like the history that I felt that we both got to bring that moment was like a history of kind of looking at Bertha and being, ‘Jesus Christ.‘” he said, raising his eyebrows.

“‘There she goes again,’” Coon echoed, with a giggle.

“Which was really, really fun to play with Merritt,” Spector said.

In addition to welcoming Merritt Wever as Bertha’s sister Monica, The Gilded Age Season 3 Episode 4 also introduced the Duke’s sister, Lady Sarah (Hattie Morahan), and Andrea Martin as a psychic whom a grieving Ada (Cynthia Nixon) visits in an attempt to reach her dead husband Luke (Robert Sean Leonard).

“So we loved having her,” Coon said, “as well as all the other marvelous Broadway actors we got to add to our company this year.”

“It’s just…it’s an embarrassment of riches, truly.”