While speaking with Deadline, the 18-year-old actress detailed her on-and-off-screen relationship with her "Enola Holmes" co-star, and shared how it differs from the friendships she has with her "Stranger Things" cast members.
In the "Enola Holmes" films -- the second of which hit Netflix on Friday -- Brown stars in the titular role, while Cavill plays her older brother, the famous detective Sherlock Holmes.
When asked to compare the "camaraderie" she shares with Cavill versus her "Stranger Things" co-stars, such as Noah Schnapp and Charlie Heaton, Brown described her relationship with Cavill as more being "adult," noting that their friendship includes "terms and conditions."
"It's different because I grew up with Noah and Charlie. I met them when I was 10. So, for me, it does feel like your schoolmates," Brown told Deadline. "And with Henry, it feels like a real adult relationship. Like a really good friendship, a really healthy one. One that we have terms and conditions. I know Henry. He has terms and conditions with me. I'm not allowed to ask about his personal life. It's like, 'Millie, shut up. No.' And I'm like, 'Understood.'"
"Whereas with the 'Stranger Things' kids, it's different," she added. "There's no boundaries because it's like we're all siblings. But with Henry, he's very strict with me, which I appreciate."
Also during the interview, "Enola Holmes" 2 director Harry Bradbeer and Brown spoke about how the latter and Cavill were able to create their sibling dynamic, with Brown sharing that she had to "pull [Cavill] out of his comfort zone" since he doesn't have any sisters.
"In a way, Henry, like Sherlock, has a very rational approach but is learning more and more to have fun and to be spontaneous," Bradbeer told Deadline. "And of course, Millie and he had this very interesting, enjoyable dynamic where they’re always poking at each other. And Millie tickles him up a little bit and surprises him. And he goes with it."
"He does," Brown agreed in response, adding, "It's shocking because he doesn't have any sisters. So, for him, it must be completely different. I have a sister, a brother, and an older brother. So, I'm very much used to that kind of dynamic. I had to implement a lot of that into my relationship with Henry offscreen and onscreen and just pull him out of his comfort zone."
Bradbeer said that he and Cavill likely enjoy working with Brown so much because they both "don't have little sisters and would've liked to have little sisters."
Per Netflix, the logline for "Enola Holmes 2" reads: "Now a detective-for-hire like her infamous brother, Enola Holmes takes on her first official case to find a missing girl, as the sparks of a dangerous conspiracy ignite a mystery that requires the help of friends -- and Sherlock himself -- to unravel."
"Enola Holmes 2" is available to stream now on Netflix.