The actresses chat and laugh easily together, a contrast to their characters' often tense exchanges in the drama's third season, released this week. Sibling rivalry and loyalty within Britain's House of Windsor are key elements, involving the steady Elizabeth and her flamboyant sister as well as Elizabeth's two older offspring, Charles and Anne.
Margaret, described in one episode as essentially a leading lady forced to play a supporting role, is upset over allowing her personal life to be constrained by duty (last season, she bowed to pressure to break off an engagement) without benefit of glory.
"Why are you so jealous of me? Why?" said a smiling Colman, helpfully — and teasingly — paraphrasing a reporter's question about Margaret for Bonham Carter. "How do you cope with being No. 2?"
It's "very, very hard," Bonham Carter parried back.
"I think it's a very fascinating sort of relationship, though, isn't it?" Colman said, and her castmate turned serious as well.
"It is, and so common to any family, whether you're a queen and a princess: How you define each other, or how somebody's defined by your position in the family and whether you are younger or an older sibling of the same sex," Bonham Carter said. "I'm lucky in my life. I have two older brothers and I'm the youngest. So I think my life wasn't complicated by it."
With Elizabeth and Margaret, "The Crown" has "definitely gone through the whole sibling competition," she said, noting that it is creator-writer Peter Morgan's dramatized version of their relationship. Margaret died at age 71 in 2002; the queen is 93.
"There is a difference between the real ones and 'The Crown' Margaret and the queen," Bonham Carter said. "I met lots of people who knew the real Margaret, and they said that they really did love each other. There was enough of the affection and the positive support that Margaret was to the queen."
The fictional pair do behave more warmly toward each other than in previous seasons, with Margaret's wrath instead memorably directed at her husband, Antony Armstrong-Jones (Ben Daniels), and Elizabeth reserving her steeliness largely for her son and heir to the throne, Charles. In one scene, his youthful lament that he wants his voice to be heard earns him a cutting rebuke from the queen.
The beleaguered Charles fares better with his supportive and spirited sister, Anne, part of the Windsor generation that's adjusting to adulthood and their royal burdens in the tumultuous 1960s and '70s. Erin Doherty ("Call the Midwife"), who plays Anne opposite Josh O'Connor's Charles, said plunging into an already popular series helped them bond.
"We met in a rehearsal and the sibling banter was just there, and I genuinely feel like he's one of my best friends," Doherty said. "I think because we're of similar ages in this really crazy whirlwind of an experience, I feel like we kind of, in real life and on screen, have to support each other."
O'Connor ("The Durrells in Corfu") noted that he and Doherty both studied acting at the prestigious Bristol Old Vic Theatre School (as did Colman, all at different times), which may have contributed to their "good chemistry.
"There's something about a kind of actor that's brought through that (program), and we got along really well," O'Connor said, then added: "I think everyone who's seen (their relationship) creatively has liked it, and there might even be a bit more of it in series four, which would be really nice."
Colman, who stepped in this season for the original Elizabeth, Claire Foy, is careful to note that "The Crown" is an imagined version of private lives. "I can't say this often enough — it's us doing our acting job, us in a studio. From an actor's point of view ... it's a part that I'm playing and it's a part that's written beautifully by Peter (Morgan)," she said, politely but firmly.
For practical reasons, Colman appreciated the advantage of playing an 18th-century monarch in "The Favourite," which earned her the best actress trophy at this year's Academy Awards and its British counterpart from BAFTA.
"I find it much easier knowing that no one can say Queen Anne didn't sound like that. Everyone's a critic because everyone" can vent online, she said. "You have to let that go. It's an acting job."