“It’s a bit loud, isn’t it?”

Vanessa Kirby, the spirited British actress who plays Princess Margaret on The Crown—and provided the main heartbeat (and heartbreak) of the drama’s first season—is speaking about the colorful houndstooth suit she is wearing inside a Beverly Hills hotel room on a recent Sunday morning.

“I thought it was suitably Margaret,” she smiles.

Kirby proceeds to prepare her cappuccino—only to accidentally dump about a gallon of Stevia into it.

“Ugh, it’s going to be disgusting . . . like dessert,” she laments. “Never mind, I’ll just drink it anyway. Margaret would.”

Another beat, then Kirby cracks up, imagining how the rebellious royal might have actually reacted to this situation: “She wouldn’t drink it. She’d send it back in a fury. In a fury!”

You can’t blame Kirby for being so Margaret-focused. She has now played the tragic royal on 20 episodes of television; The Crown’s second season premieres December 8. And Kirby’s character devotion runs so deep that her home is currently wallpapered with photographs of Queen Elizabeth’s younger sister.

“I’ve got pictures of her everywhere, which I think is quite disturbing for anyone who comes over and doesn’t know that I play her,” smirks Kirby. “She’s in my loo. I’ve got a picture of the front cover of Tatler with her and Elizabeth on horseback, when she’s like 13. Anyone who goes in would be like, ‘This is such a granny loo.’ I have another beautiful picture of her with Elizabeth at the Royal Variety [Performance], and she’s got this really low-cut top—my favorite picture ever—and a long cigarette holder. And Elizabeth’s wearing this kind of, like, nun’s outfit.”

“The reason that I have that one on my wall in the bedroom is I was hoping that by osmosis, I would absorb some of her, and also because it really defined . . . how the sisters couldn’t be less alike. I really wanted to look at that when I’d wake up, and maybe channel a bit of it.”

The osmosis must have worked, because when Kirby met one of Margaret’s ladies-in-waiting, they had only kind words. Well, mostly.

“She said the performance was perfect . . . which was so flattering, I couldn’t believe it. I nearly died,” says Kirby. “She said, ‘The only thing was that [during Elizabeth’s] wedding, you were a little bit too bubbly. Margaret would’ve taken it much more seriously.’”

Of the lady-in-waiting, Kirby continues, “Oh my God, I was dying to take her out for lunch. I did actually ask her, and she said yes, but she was a bit reluctant. I didn’t want to push it because, actually, I’d probably drill her for so much information.” (Though the royal family has not officially commented on The Crown, Kirby also tells us that her friend met one of Queen Elizabeth’s granddaughters: “Princess Eugenie—or was it Beatrice?—who said that her granny loved it.”)

Before filming The Crown’s first season, Kirby was careful not to read about Margaret past 1955—when the first season ended. So when it came to preparing for The Crown’s second season, Kirby said that she simply “picked up all the books that I had under my bed” and read on. The actress found that there were more accounts of Margaret during the 60s than the 50s to pour over, because during that decade, “she got bolder. She got braver. She started going into more suburban London as opposed to staying within the palace.”

Margaret’s trajectory in The Crown’s second season hinges on the princess’s relationship with her rebound love interest Antony Armstrong-Jones (later known as Lord Snowdon)—the photographer she marries after discovering that her first love, Peter Townsend, is engaged. But the new episodes only chronicle the marriage up to a certain point.

“The marriage did start getting really difficult, and I heard a lot of stories about him not being very nice to her. But I had to try to ignore those and concentrate on them falling in love and what that would’ve felt like for her—how liberated she felt to be with somebody who was so unroyal and didn’t approve of her family.

“The second season for me is Margaret’s attempt to find herself. . .I think she thinks she’s done it with Tony, and later on she realizes it’s not the case.”

Kirby says that The Crown had a difficult time casting the role of Lord Snowdon because production needed someone who was not only a match in strength for Margaret, but someone who could also intimidate her.

Matthew Goode, who ultimately got the part, “is perfect,” Kirby explains, because he telegraphs Snowdon as “sort of strange and sexual and predatory, as well as elusive.” Goode and Kirby summoned crackling chemistry in their scenes—one of which begins with Margaret arriving at Snowdon’s studio alone for an unofficial portrait sitting. Filming the intimate scenes, with director Benjamin Caron, mirrored what Margaret must have felt when she finally began venturing outside the palace.

“Suddenly, it was like Margaret had her own little world, and that was really interesting to explore and something that us three did together. And we loved it. We just laughed from morning to night with Ben, the director. We had a little threesome. I wouldn’t even mind if anyone watches a second of it, ‘cause I just had the happiest time.”

If there is one signature of Margaret’s, it is her ever-present cigarette. Though Kirby detests the herbal props she chain-smokes while filming—“God, they give you such a headache . . . we had boxes of them and just drilled through all of them ‘cause we were doing take after take after take”—she respects Margaret’s rebellious spirit, which led her to embrace the habit. “When she was 15, she tried smoking,” says Kirby, an expert in this area. “She lit up when she was 17 at the Royal Variety [Performance] . . . in public. No royal figure had ever done that.”

Because the cigarettes are such a Margaret hallmark, she and Caron “had this massive, long conversation” about whether they should show the princess puffing away in a later episode while visibly pregnant.

Though they determined that Margaret probably would have smoked while pregnant, they figured the imagery would be politically incorrect.

“We decided not to do it, and I didn’t know what to do with my hands,” Kirby says, explaining that she swapped the cigarette out for another Margaret vice. “I poured myself a large whiskey. I was like, this is the only way.”

The second season does not delve into the implosion of Margaret’s marriage, which, while a devastating period of life for Margaret herself, would have been incredible material for Kirby to sink her teeth into. (The third season of The Crown, which jumps forward in time, will instead pick up with a new cast of older actors—led by Olivia Colman as the next Elizabeth.)

“I was so desperate to do further on . . . because it’s going to be so fun [to enact] when their marriage starts to break down. You see the beginnings of that in episode 10. I kept saying to [series creator Peter Morgan], ‘Can’t you put in an episode where Margaret and Tony have a big row, and she throws a plate at his head?’ I’m so envious of the actress who gets to do it.”

Kirby says she was so determined to continue portraying Margaret that she even told Morgan, “‘We need to do a spin-off.’ You actually could do 10 hours on Margaret because she’s so fascinating. There’s so much to her, and she’s such an interesting character. I know that parts like this hardly ever come along.”

Though Kirby has filmed her final scenes as Margaret—and had a proper cry to commemorate the milestone—she hasn’t yet taken down her Margaret photos at home.

“Actually, a friend just gave me this amazing one of her on the beach that Tony took, and she’s really free and wild and the lights are in her eyes. It’s a really iconic picture . . . hair really messy and she looks so amazing. I’ll probably have that one up forever because something about her spirit, I just . . .” Kirby takes a moment to find the right words, her eyes sparkling with a tear or two. “I feel really honored to have gotten to know it.”