Millie Bobby Brown has a "healthy" and "adult" relationship with Henry Cavill.

The pair play brother and sister in 'Enola Holmes' and the film's sequel and Millie has opened up about their friendship - insisting they have a strong bond despite their 21-year age difference with the actress applauding the 39-year-old 'Man Of Steel' star for being "strict" with her.

The 18-year-old actress told "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.

Millie then explained that one of Henry's conditions is that she's banned from asking him about his private life. She added: "I’m not allowed to ask about his personal life. It’s like, ‘Millie, shut up. No.’ And I’m like, ‘Understood'."

She went on to insist her relationship with Henry is very different to her friendship with the rest of the young cast on her Netflix show 'Stranger Things'.

Millie explained: "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."

She added of the actor: "I would say Henry ... is a problem solver. He’s a very rational man. Me, I’m a bit manic. I’ll try everything in order to solve something. Whereas he usually just gets it dead on right ... "

Millie also explained they have a special dynamic because Henry doesn't have any sisters in his family. She went on: "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."