She is one of Britain's most successful exports to Hollywood: a young woman who shot to fame at just 12 years old and has still managed to avoid the usual pitfalls of celebrity.
Still, when Stranger Things star Millie Bobby Brown recently announced she has adopted a baby girl with husband Jake Bongiovi, there were audible gasps in one meeting of high-powered talent agents, one of whom had worked with the 21-year-old star.
'I mean, good for her, but who on earth adopts a child at 21?' a dumbfounded agent told The Mail last week.
The person continued: 'She's at the top of her game professionally, so this wasn't anything anyone saw coming for Mills (her nickname). She deserves every happiness but, as usual, she is writing her own rule book.'
Indeed, she is. But then Millie Bobby Brown has always done things her way, and always been wise beyond her years - as I have myself witnessed.
I met her nine years ago, when she'd just turned 12 and she skipped into the marbled lobby of The London Hotel, a five-star establishment just off LA's infamous Sunset Strip. She was tiny, 4ft 11in, wearing shorts and a floral T-shirt, her hair in the distinctive, shaven crew cut necessary for her role as Eleven in Stranger Things.
Millie was in the middle of filming the first season of the hit Netflix drama, but even then, she was different from any other child star I'd met.
Our chat for the Mail was her first ever sit-down interview, but, far from seeming nervous, she seized control of the room and everyone in it - including me.
I was there alongside her then manager Melanie Greene, a Hollywood legend. Also present was her father,r Robert, who shifted from leg to leg and who, in complete contrast to his young daughter, seemed ill-at-ease, something Millie grasped immediately.
'Dad, why don't you go upstairs to the room and be with Mum [Kelly],' she told him in a soft but commanding tone. She added: 'I'm fine. I don't need anyone with me.'
Robert did what he was told, and with that she proceeded to check where I would be most comfortable sitting. Did I want a cup of tea? Water? Where would I like to begin?
I was astonished. For a young girl, particularly one new to Hollywood, she was so poised and confident in her own skin - without being brattish - that it has stuck with me ever since.
Stranger Things, in which Millie plays a girl with telekinetic powers, became a global phenomenon with its fifth and final season starting later this year.
Thanks to the show, Millie has built a reported €23 million fortune. There have been three movies including two Godzilla films which have raked in nearly $1 billion at the global box office.
But Millie continues to shun Hollywood convention. There is no Hollywood Hills mansion, burly bodyguards or trainwreck lovelife. Instead, by the age of 20, she was already married, to long-term boyfriend Jake Bongiovi, 23, the son of rock legend Jon Bon Jovi.
Their wedding was small and discreet, and the newlyweds live in a remote ranch in rural Georgia, US, with rescue animals including a donkey called Bernard and a therapy dog named Winnie. Friends say last week's adoption announcement was no surprise.
'Millie marches to the beat of her own drum and always has,' said one woman who has known her for years. 'She's always been mature and a lot of that was because of her upbringing. She was her family's main breadwinner from an early age.
'It doesn't matter how stable you are, that's a weird thing for any child. Millie always said she was determined to give her kids the normal childhood she never had and that's why she and Jake have started young. She's a collector of lost souls. She has been rescuing animals, people, things since she was a child.'
Indeed, many are convinced that her chaotic, nomadic childhood has made her determined to recreate a stable family for herself, at the earliest opportunity.
Millie was born in Marbella, the third of four children, to British couple Kelly and Robert Brown. They'd moved to Spain to work in the real estate business, and to be close to Robert's parents, who ran a restaurant there.
When that didn't work out, the family went to Florida where Robert developed a tooth-whitening business which, again, didn't amount to much.
During my first meeting with Millie, Robert came down towards the end of the interview and told me how Millie had always stood out as different. He said: 'My other children would watch cartoons but Mills watched musicals - Chicago, Moulin Rouge, Annie and Bugsy Malone. She'd belt out a tune. She was performing from day one.'
When Florida was a bust, the family returned to Britain, settling in Bournemouth, where Millie attended Pokesdown Primary School. It was here she caught the acting bug, as she told me: 'I was annoying my father one Saturday and he said, "We need to find you something fun to do".' She enrolled in stage school and was so precociously talented that an agent suggested the family relocate to Los Angeles.'
'It was a huge leap of faith,' says someone who knows the family. 'Kelly and Robert have four kids and they rolled everything on this huge gamble. 'They put everything on Millie hitting it big. That's quite something.' Especially for Millie. The family ran out of money and had to borrow from close friends. The insider adds: 'There was a huge amount of pressure. When she went to auditions she was fully prepared. She wrote "thank you" notes when she didn't get the part. People remembered her because she was a little girl, yet so poised and polite.
'Then Millie got Stranger Things and they hit the jackpot.'
They still faced teething troubles, though. Robert reportedly tried to manage his daughter's early career and was said to be demanding $100,000, up front, from producers and agents to even get in the room with Millie. This was later said to be 'a misunderstanding' and an insider said Millie's 'talent and charm' trumped any perceived 'misbehaviour' by her father: 'That little girl would walk into a room and have everyone eating out of her hand within minutes.'
In an interview earlier this year, Millie admitted being a loner who chose to distance herself from social media - and the pressures of Hollywood - for her own sanity.
And she told Vanity Fair magazine: 'I didn't go to school [she was educated by on-set tutors], so I don't have the best social skills when it comes to people my own age and friendships.'
She met Jake, also an actor, when she was 17. The pair had dated quietly before marrying at Villa Cetinale Roman, a baroque villa in Tuscany, Italy, last year. They were spotted pushing their daughter (rumoured to be called 'Ruth' after Millie's late grandmother) in a stroller last month.
During an appearance on the Smartness podcast before this week's adoption news, Millie said: 'My mum had her first child at 21 and my dad was 19. Since I was a baby, I wanted to be a mum. Jake knows how important it is to me to start a family.
'It's a huge thing and Jake was like, "We cannot do that until we get married", so that was his thing. I'm one of four, he's one of four. We really want a big family...'If we're not fully invested, then what's the point? We have to be and we always have been.'
The final series of Stranger Things is out later this year - but Millie's greatest adventure is just beginning.
