Working with Cavill, unsurprisingly, is nothing like the set of Stranger Things

The 20-year-old first worked with Cavill on Netflix's mystery movie in 2020, and the pair returned as Sherlock Holmes and his younger sister for the sequel, Enola Holmes 2..

Brown told Deadline that there were "no boundaries" on the Stranger Things set because it felt like she and her co-stars were "all siblings", but things are a bit different with Cavill.

Because she didn't "grow up" with Cavill - who is more than twice her age at 41 - like she did on set with Schnapp and Heaton, things on On Enola Holmes,  are a bit more reserved.

Brown explained: "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. And with Henry, it feels like a real adult relationship. Like a really good friendship, a really healthy one."

She said her relationship with the Superman actor has "terms and conditions".

"I know Henry. He has terms and conditions with me," she said.

"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. There’s no boundaries because it’s like we’re all siblings. But with Henry, he’s very strict with me, which I appreciate."

Brown said her experience on Enola Holmes was "pivotal" for her acting career and praised director Harry Bradbeer's "attention to detail", saying that is what "makes the film so immersive".

"Everyone on set knows Harry and his way and his spirit. The dedication to the film is unlike all of us put together. So yes, it does come down to performance, but it also very much comes down to directing and being able to have a connection with your director."

"It’s a dream come true," she continued.

Brown said she was learning "many things" on set, "because I’m an upcoming young woman and that is a real learning curve for me".

She added: "This is a very big pivotal moment within my career and my life. This is the first role I’ve really led."

David Thewlis, Louis Partridge and Susan Wokoma star alongside Cavill and Brown in the film.