If the first season of “The Crown” probed the sibling rivalry between Queen Elizabeth (Claire Foy) and her sister Princess Margaret (Vanessa Kirby), the second season takes the gloves off. The two women are driven even further apart as the ever-more headstrong Margaret continues her ill-fated search for love.

Yet Kirby says the more she’s gotten to know about the Princess, the more she’s fallen “in love” with her. But that’s not to say she’s been able to watch it yet. “I think I might watch it over Christmas with my family and skip my episodes,” she says. “I think because I care so much about Margaret. It’s a bit overwhelming. it’s such a special thing to me that has a lot of meaning.”

Sadly, Kirby’s reign will end as the series gets recast for the third season, which will cover the next decade in the royal family’s life. (Olivia Colman has already been announced as the new Queen.) “I just love her,” says Kirby. “I don’t think I’ll ever have a better part.”

This season is so much more about Margaret — we get to spend much more time with her.

It was exciting. And I think, God what a privilege to play somebody and got to know them quite intimately over that series one and two. I get to go deeper with her. I get to grow up with her and get to know her better. It was really exciting to travel through a little journey of life a little bit more. I felt so lucky. We always knew it was going to be two seasons [for the initial cast]. For me they are there own entities in a sense that it’s different for different versions of Margaret at a different time in her life. But I knew it would ever only be those two so I’m just going to try to make the most of every minute.

Were there things you wanted to accomplish this season for her?

I always felt like I had a responsibility, to set it up for [the next actress] and set up the real person in a sense because all the things I heard the most about her was she was this kind of tragic figure later on in life. I didn’t really know much but I knew that she was the Queen’s sister who wasn’t around anymore. So I felt quite ashamed actually when I learned lots about her and began to totally fall in love with her. I mean, utterly fall in love with her. Because I realized that I didn’t know the young woman behind this adult. And this older figure that had become tragic in the public eye. I felt like I had a responsibility to show who the girl was really and how somebody becomes hard or however everyone perceived her. Icy. Cold. Guarded. And a bit of a battle axe. How does somebody become that? The second season for me felt like a deeper exploration of that. Also felt like the beginning of a hardening process. Because it was tough. Tough losing her dad, tough being in that family, tough being innately inferior just because you’re born second and your sister is treated differently. I felt a definite responsibility to not play the end. I hope that the public sees her in a different way now and even if it’s just a handful of people, I would have felt proud of that. And also the actress that plays her next. I hope in some way I’ve done sort of justice to what she might do.

Do you have any idea who’s going to play her next?

I asked (showrunner) Peter (Morgan), “Can you tell me?” And he was like, “I would but you would tell everyone.” I said, “I know. That’s so true. Dammit. You know me too well!” I think they’re still in conversations. I don’t have the foggiest idea. I can’t wait. I think it’s so exciting for that person.

What do you think of Olivia Colman?

Amazing. I mean she’s a national treasure in her own right and so feels aligned in a way it feels right. That somebody that so loved and so talented and so respected like the queen really is taking over from someone as incredible as Claire. I mean, God, what a hard act to follow.

You’re a hard act to follow, too.

I’m just excited for the next person to do it because then we can talk about her. I only did my research up to 1964 and I had to stop because I just didn’t want to ever [play the end]. There are things beyond that I would have loved to have played, like she got morekind of sassy and even more outspoken and more demanding and aggressive in some ways. As well as probably more fragile and vulnerable. Drinking and arguments. And crazy rows with Tony. I would have loved that. But I really had to contain myself and not go past that point because that’s not my job.

What advice would you offer the woman who comes next?

Just have the best time. And get the lovely wonderful head of props, Mark, to light your cigarettes for you. Because then you save half the smoking. You share the load. I felt so terrible actually because by the end both of us were wheezing in the corner.

You were smoking real cigarettes?

They were herbal ones. But in the 1950s they don’t have a filter. And so it was very strong. And lots of herbs go in your mouth all the time. We tried all the different flavors to make it better. But it was so much a part of her behavior. Her way of being was a cigarette as her weapon. Both armor and weapon. There was one scene at the end of episode 10 where I had to not use it because she was pregnant. I didn’t know what to do with my hands. So I just poured myself a massive drink.

How did you get into character? Did the smoking help?

As soon I lit a cigarette I felt like her. It really helped. But what was harder was finding her anger and finding the pain. Which I think translated into anger and the anger always runs alongside. I think underneath fear and insecurity and pain that wound that she has. Many wounds, how to play that right. There were some times during season two that she became such a different person to season one. I worried that she would just seem so raging and very unlikable and that people wouldn’t be able to have empathy. That was a challenge and I felt conscious of that. Because I did feel like her pain translated into coldness or hostility. It was negotiating those.

What made her so angry?

It’s really hard! I bet the Queen and Margaret, wherever she is, are like, pfft, you don’t know what you’re talking about. I always felt that it was such a weird set of circumstance wasn’t it. Edward falling in love with Wallis Simpson meant that he gave it up. Such a heavy decision for him. Which means that then George takes over. When you are little girls this stroke of fate, this chance happens. And then because of that inherently your sister is treated differently by the public, by everybody they meet, by their parents. She’s literally groomed and looked at in a different way because she’s heir to the dynasty of your own family. And you’re not. Margaret was spoiled in a way because they tried to make up for it. But if you’re hearing at parties, your parents say to their friends, “the right one was born first.” She heard that all time. I mean, can you imagine? And then your dad suddenly dies and suddenly your life is totally different. And not of your own volition and choices. Their sister rivalry is an intensely interesting thing to examine. Endlessly fascinating. Because it’s just such an unusual position for two human beings to be in and only two people in the world have gone through exactly that.

That conversations are so fraught, so tense — there’s so much unspoken stuff that happens between the two of them.

It’s the total unspoken stuff that was really interesting. I think that began because Peter said this is a family that don’t talk about their problems. They don’t talk about what’s going on. There’s a really good example where Margaret is in her the darkest place and the mum comes in and goes, hello darling and opens the curtains, and says, what a mess you’ve made and doesn’t say, oh my goodness you’re in pain, what can I do to help. No one says that. Everyone just gets on with it and she’s already talking about who she can marry from the aristocratic circle, when Margaret has just been rejected and humiliated. And beginning the first episode Margaret was trying to break away from this establishment that she’s so essentially part of and is within her. And yet has caused her so much pain. In episode 7, the scene where the baby’s has been born and Margaret saying, can you please finally give your word to let to me marry Tony. I had this idea that I really wanted to play like Margaret’s finally found what she’s been looking for. She’s got this sense of reconciliation and forgiveness and peace. And it didn’t work at all because actually the truth of it is that at least in our imagined version of events,they’ve never had a conversation. Elizabeth’s never really said I’m so sorry, I’m with you, can I help heal us and can we to go to therapy. I don’t think the forgiveness has reached that point. Maybe it will in the future seasons. But my feeling is that Tony is not a salvation for her. I think she thinks it is. But he’s not the man that she needs him to be, that she wants him to be.

Do you think she was in love with him?

I just want her to be happy. I so long for it. Like the ending of a movie that you don’t want to happen, like “Titanic”? I just wanted it so much for her. And I loved reading the early pages, their little courtship. But I realized that Margaret  has this wound. She’s incredibly raw. She said herself, I’m unhinged without Peter, I’m lost without Peter. So she’s drinking, she hasn’t found her place. Her sense of self is totally fractured. And she meets somebody in that state. So you get these two kind of wounded people. Is that going to be healthy, stable long term sustainable love? I don’t know. That other thing that really broke my heart was when she gets the letter from Peter Townsend (saying he’s gotten married). And I just said don’t show me what’s in the letter until we film it. And I read it and it just killed me. That was pretty much one of the hardest moments for me to film. Even now thinking about it makes me upset. That’s what motivated her (to marry Tony). It was a week after she had that news. It was factual that she then put out the announcement to marry Tony straightaway. It’s a mixture of don’t humiliate me first, I’m not going to have people find out. But also you know I’m going to do it myself. Lot of those little things gave us indications about what was happening inside.

Do you think Peter was the love of her life?

It’s hard to know isn’t it. I mean I read so many things that people said she would have got bored with him and he was too old for her. … But that’s the question if she were alive I would have loved to have asked her, do you still love Peter? Did you still love Peter? I just grew to love them both really. How mad it was that this old set of values and protocols and really defunct ways of belief systems stop two people (from getting married). Everyone’s asking us about Harry and Megan and that’s what’s so cool. She is divorced and no one has even mentioned it. Love whoever you want to love. We were just in Australia and they just passed their marriage equality law. You should choose who you love. And I hope that Margaret story only illuminates that.

Do you think the sisters every truly reconciled?

I had always heard that they were really close and that Margaret had lots of pictures of her sister in her toilet. So I don’t know. She obviously didn’t mind weeing with her! Our story is dramatized obviously. So it’s really hard to speak about them as real people when we actually have no idea about their thoughts and feelings. Your sister has got this job and hasn’t chosen this job. That’s a really conflicting thing, isn’t it. I would never not want to be a princess. I can’t give it up to be Mrs. Townsend and my father was the king of England. My sister is the queen. And yet I want to be me. How do I be me within  a system which hasn’t allowed me to do the choices and the freedom to be me. I can’t imagine her abandoning it completely and not finding ways to still love her sister.

This season they both face romantic problems, yet they can’t confide in each other.

The only way they address it is Margaret being antagonistic and saying, oh I’ve heard about Philip and these ballerinas haven’t you. Or, look at him there on the newspaper, looks like him doesn’t it. Elizabeth had the freedom to marry who she wanted at 21. And Margaret watched her walk down the aisle with somebody that nobody approved of. And she did it anyway. He was like the rogue choice and she loved him so she got him. In episode 8 of the last season Margaret says, at least you have a role very clear set of rules. All you have to do is follow them. And the Queen says, at least you have freedom.

Did that photography scene with Tony really happen?

Yes, she said to him, can you take my photograph. And he said, yes, come to mine which is already, she’s not on neutral ground, she’s not in her comfort zone. We really felt that. We really thought about what she’d wear. I always imagined Margaret spending a long time choosing because she has the time and she has the natural flair for it, unlike her sister. And she expresses her internal life through it. I think it’s her kind of sexual awakening in a way. Suddenly she’s accepted an invitation to got to this man’s house. It’s incredibly exposing having you5 picture taken especially to somebody that you know is already wanting to slightly take down what you represent. So you know you’re going in there to be stripped. And so I chose this little blouse that was lacy — I wanted a suggestion of sensuality without dressing up too much or going over the top. She would have tried to look cool. But I also wanted to suggest that she was open to something with him. And that she was wanting it. Needing it. Craving it. A whole new energy in her life to awaken in her, and I think by the end of episode 4 she is kind of lit up in a way that she hasn’t been for a long time, maybe since before her father died.

What was it like filming the scene where she trashes her room?

In the script it was, Margaret does a melancholy dance. And that was it. Just one line. And I was like Margaret never just does melancholy. She doesn’t just do what everyone else does. She’s somebody that has such an extreme range of feelings whether it’s static highs where she’s flying or whether it’s the real crushing depths. I always imagined all the moments where we don’t see her, like what’s she like after Churchill’s told her off. She’s holding it together when he’s doing it and then what was she like when she was at home? Because her feelings are expressed so easily. And she doesn’t really have a filter. So I was like,she’s not just going to dance around the bedroom. She’s going to trash it. So we worked with this great director. And then we found this song. And on the day, it was six hours of just trying to go there. It gave me whiplash. It’s only like a 20 second sequence in the end but it was a long time doing it. It was a great expression. I was glad we get to see her Margaret behind closed doors, behind the facade, behind the mask, behind the guards and the armor. God, I love her!

Did you take anything from the set?

I took a little ring, which we imagined Peter Townsend gave to her before he left for Brussels. I have that at home. Apart from that we can’t really because all that stuff is now being used for exhibitions. I couldn’t steal a ballgown — I’d wear it out on Saturday night!