Millie Bobby Brown and Louis Partridge on belly laughs, sibling vibes and Enola Holmes

It is rare to meet two co-stars whose chemistry is obvious before the interview has even begun but before I ask Millie Bobby Brown and Louis Partridge a single question, they are already laughing together.As they return for Enola Holmes 3, they say that off-screen friendship has helped them bring more ease and affection to Enola and Tewkesbury's developing relationship."We realised we don't do much prep for some of the scenes - we learn our lines and rehearse and it's not that we don't take it seriously but we're really able to be in it," Partridge says. Brown laughs as she jumps in, turning to Partridge with the kind of mock-seriousness that suggests this is a familiar routine between them.She says they bring out each other's sillier side and they spend most of their time on set "belly laughing about the most random things". "People will say to me, 'I just met Louis Partridge and I had a really interesting conversation, he's a really smart guy. I'm like, who? Louis Partridge is a smart guy? When?" We definitely regress into our younger selves." Partridge, 23, smiles at this and tells me there is something almost sibling-like about their dynamic, which may explain why they are so comfortable teasing each other."We were just remarking that we look like brother and sister," he says. "There's definitely a bit of that relationship between us."