Helena Bonham Carter distills the essence of Princess Margaret for ‘The Crown’

Helena Bonham Carter has played a number of royals, including her Oscar-nominated role as Queen Elizabeth in “The King’s Speech.” But it isn’t the pomp that draws her, it’s the writing.

In fact, when “The Crown” creator Peter Morgan asked Bonham Carter to take over the role of Princess Margaret for Seasons 3 and 4, “I said, ‘Well, I need to see a script.’ And he said, ‘What do you mean you need to see a script? One, we’re a massive hit, and also Olivia’s not asked for a script,’” referring to his new Elizabeth II actress, Olivia Colman. “And I said, ‘I’m sorry, I’m not like Olivia.’ So the sibling rivalry’s already started.

“But I need to know if I’ve got something to bring to bear to her,” she adds. “It’s the writing that does it.”

She was also late for their first meeting. “He said, ‘Jesus, I’ve chosen the right person.’” The actress wasn’t so sure. Margaret’s Season 1 and 2 incarnation, actress Vanessa Kirby, had just won a BAFTA for the role. “I thought, ‘Well, how do I follow this?’” Bonham Carter recalls. “And then I thought, ‘No, I can do short.’ Vanessa’s, like, endlessly tall. And I’m nearly as short as Margaret.”

And that, for her, was an early key to playing the role.

“A lot of her behavior was trying to make herself as tall as possible,” she points out. “Her wedding tiara was four inches high. She had the seat of her car raised. She always sat amazingly bolt upright. She made herself as tall as she could be.”

Meeting in a hotel suite on a brief foray into Los Angeles from London for the show’s third-season premiere, Bonham Carter, a Golden Globe and SAG Award nominee, combines casual self-deprecation with a scholar’s wealth of knowledge about Margaret. She loves nothing more than researching a role in depth.

“My ex, Tim [Burton], used to wander in and say, ‘You’re not writing an autobiography; you’re just playing someone.’” She calls herself a swot, which translates roughly to an overenthusiastic student. But with the princess, there was such a plethora of material she was overwhelmed. “You’re given the part, and the first thing, you’re, like, ‘right, this is a great part.’ And then you’re, like, ‘Jesus, where do I start?’ You can just crawl into a small dark place and cry because there’s so much research to be done.”

She turned first to Kirby, who was generous in giving her pointers as well as a reading list. “She was so sad to let her go, which I can understand now that I’m in the position, I’m going to have to give her up to somebody else.” The role will be recast after Season 4, which they are in the midst of shooting.

The queen’s younger sister has been written about endlessly, and often negatively, over decades of media coverage. So after consuming all the written accounts, Bonham Carter turned to those who knew Margaret best: her friends.

“If she were as ghastly as the press portrayed her, she wouldn’t have as many friends as she did, and they were really happy to talk about her because they genuinely loved her.” She learned of Margaret’s economy — with words, with movement. “If she didn’t have to answer, she was very quiet. She wasn’t an introvert, but she was removed.” And sharply observant — according to one of her friends, “she was like a bird of prey.”

Bonham Carter’s own friends and family assisted as well. Her aunt, a graphologist, analyzed Margaret’s handwriting. A close friend who’s an astrologer worked up Margaret’s sign. “I don’t know how it works, but, boy, is she perceptive. She immediately said, ‘It doesn’t matter about where Margaret came from, this woman isn’t capable of not saying what’s in her head.’ That’s something that gave her a lot of trouble.”

Stories of how a medium relayed messages to Bonham Carter from Margaret’s spirit have already made the rounds, but Bonham Carter insists that she wasn’t asking for the spirit to show up. It just happened while she was doing other work with a friend who’s also a psychic.

“I’m open to everything,” she says, aware it proves amusing to others. “I don’t swear by any of this, but I do feel that there’s a lot that we don’t know. And I’d like to think, for all sorts of reasons, that people carry on in some different form, and if I’m carrying their name, I do feel that I want to have their kind of blessing.”

Margaret gave her more than that. She gave notes: Get the smoking right, and “You’re going to have to scrub up,” Bonham Carter relates, laughing, fully cognizant of her reputation as an eccentric dresser.

Those external elements were crucial. The right pair of shoes could change her behavior. “The wig is everything too. You get the silhouette right.” In addition to “The Crown’s” hair, makeup and costume departments, she praises the on-set researchers. “When I was doing Episode 2 with Ben [Daniels], who’s amazing as Snowdon, their sex life was very colorful — with other people. I was saying, ‘Hang on, who was having an affair with whom at this point?’ And within a day you get a whole dossier.”

Her other costar, Colman, was amazing as well. “We feel very supportive of each other, very at home,” Bonham Carter says. “We probably were [together] in some former life.” She notes that their styles could not be more different. “She will not do any chat, or analyze. She wants to go all instinct.”

That goes into Bonham Carter’s mix too, along with all the research. Then comes the distillation. “It’s like making a perfume or doing a sauce, getting down to something that you feel defines them. Like a collage.” She pauses a moment. “I should do a collage of her!”