You fear the worst on your way to meet Kristen Stewart. Tales of her sulkiness are legion. If her most famous screen character, Twilight's Bella Swan, is the girl who can't bring herself to surrender her virginity (to be fair, it's a choice between a milksop vampire and a werewolf unable to keep his shirt on), the skinny on Stewart is that she's the actress who refuses to make peace with celebrity.
Alone with her for half an hour, the worry is she'll be all monosyllables and rolled eyes.
As with many caricatures, it's true, but only to a point. Seated in a vast armchair in Claridges, her features even more china-doll and porcelain than on screen, Stewart is chatty and tomboyish, glamorous, though not in that blinding Hollywood way.
She meets your gaze and it doesn't feel like you're staring straight into the sun. Still, hints of the old seriousness linger.
Clicking her tongue, Stewart admits that when Twilight took off in 2008 transforming her from suburban slacker to international icon of love-struck teendom, she retreated into herself. Sometimes this came off as grumpy, even mean-spirited. It's taken until recently for her to recognise that.
"The thing is, movie stars aren't supposed to be like ANYTHING," says the petite 22-year-old, her patter a gushy SoCal mall-speak.
"You are used to seeing them smiling. Now, in situations where people judge you, I'm able to smile too. You feel proud of yourself and worthy to be there."
Whereas, early on she felt undeserving of the adulation?
"When something like that is thrust upon you, it's not easy to wrap your head around it," she says. "I'd done a bunch of movies up to that point. [Twilight] was something I hadn't expected. I was uncomfortable. It came off that I was ungrateful. When it was just that it was a lot for me. I always took everything so seriously.
"People wanted a five-second canned answer. I was incapable of that."
Stewart recalls attending ComicCon, the world's pre-eminent geek fest, and being stunned by the Twilight-mania.
Something big, she suspected, was about to blow up. "I didn't necessarily know my life was never going to be the same again. I knew Twilight was going to be huge ... It was so weird to do something like that. That was so bizarre. It was visceral."
As she quickly learned, global fame carries a downside. She couldn't leave the house anymore. Screaming teenagers would descend, literally in droves.
"It's gotten easier," she says. "I can walk down the street. You just have to do it differently. It's intense when you have a movie coming out. Which is cool -- it means people are talking about it. When it's in-between time, it's okay for me.
"I know everyone thinks my life must be nuts. Between movies it's not. Except when people pop out and suddenly I'll be photographed somewhere I don't expect. I always look really surprised. It's like 'oh'. And they always use the first shot.
"It's not full-on all the time. I do wish I could walk around a bit more. But it doesn't matter."
It must be difficult, having to always be sweet to fans. She shrugs.
"I'm nice to people who are nice," she says. "There are ridiculous people who walk around and probably think I'm a total asshole. I enjoy meeting people who are happy to meet you.
"People who don't go, 'Oh God, there's that weird novelty sitting in the corner, I'm going to take a picture of her and put it on Facebook'. I definitely give back what is given to me."
The one thing everyone -- even non-Twilight heads -- know about Stewart is that she refuses to discuss her love life.
Lately, however, cracks have appeared. In a throwaway comment to a UK lads' mag last year she mentioned that her boyfriend -- understood by the entire world to be Twilight co-star Robert Pattinson -- is English (it was the palpable chemistry between the two in a screen test that won Pattinson the part of hunky vamp Edward Cullen in the first place).
In a different interview she as much as 'fessed up to their item-hood, saying: "So much of my life is so easily Googled. I mean, it's like, come on guys, it's so obvious!" Today she wears a gold ring on her index finger, said to be a gift from her hulking beau.
Given it's an open secret, why skirt around the issue? Isn't she making a bigger deal of it than it really is? The answer, it seems, is that she's afraid she and Pattinson might end up another novelty Hollywood couple, with Brangelina, Bennifer, TomKat, etc. Who, she intimates, would wish to be one half of K-Patz?
"I don't want that," she says. "As soon as you embrace that, you think you are worth it, that it's everyone's business to know what you are doing on your Sunday afternoon.
"I think that's so embarrassing. It's not something I find interesting in other people. I don't want to be that."
Did she work all of that out in her head when she and Pattinson started seeing each other (allegedly)? She shakes her head. "At that point it was definitely not an intentional thing. I was just reacting."
In her first flush of global celebrity, Stewart caught flack for her alleged slovenliness. By this, it was meant she didn't go out dressed like red-carpet bait 24/7. After Twilight, paparazzi shots of her mooching around in skater-gear were ubiquitous.
While the actress soon smartened up and was recently named the world's best-dressed woman by a UK fashion magazine, given the choice, she'd be back in hoodies and Keds tomorrow.
"If I was a civilian, I wouldn't be interested in fashion in the least," says Stewart, this afternoon demurely turned out in a grey blouse. "If I was flipping through magazines, I would have opinions on who looks good and who doesn't. However it wouldn't be a world I would have anything to do with. It's a weird relationship you have with fashion.
"It puts you in a position to get work," she elaborates. "If you do it right, it's a perception that literally makes you more valuable.
"That's not why I do it, I am definitely honest in all my choices.
"It's such a strange thing -- if you don't have good fashion sense, it could kill you as an actor. Especially as a girl." She snorts. "It's ridiculous."
She was raised by "eccentric, weird hippie parents" in LA's San Fernando valley. Her father was a stage manager, her mother a script supervisor and Stewart grew up on movie sets.
"I would see these other kids and I'd ask 'where is their mom, where is their dad?' And I'd be told 'they're the actors, don't talk to them'. And I thought, 'I want to do that.'"
You sense her family aren't in the least intimidated by her success and that this is one of the things that keeps her grounded. "They are not impressed ... My dad is constantly telling me I should stop being so weird," she laughs. "My mom is like 'oh, just go make a good movie'."
Her first major role was in Panic Room, playing Jodie Foster's daughter. Though too young to appreciate the fact, it was a tough shoot. Notoriously finicky, director David Fincher would require actors to do up to 80 takes of a scene.
"Luckily, I was with Jodie," she says. "Obviously she's been acting her entire life. She always had my back. I had no idea it was not normal to do 80 takes of one line. Sometimes I got a little heavy. At one point Jodie said 'no, no ... she's done'. Looking back now I think, 'wow, I was really able to take it at a young age'."
Shooting on the final Twilight movie, Breaking Dawn -- Part II, finished recently (she has the bruises, picked up in an on-set mishap, to prove it).
So she has to start thinking about life without Bella. Her first significant part is as the titular heroine of the clamourous new retelling of the brothers Grimm's classic fairtytale, Snow White and the Huntsman.
The movie could be seen as playing it safe, proving she can carry a tween-friendly blockbuster on her own. Anyone who has seen Stewart own the screen in quirky, smaller features such as Adventureland and The Runaways will be disappointed she's leaped from Twilight straight to another summer tent pole.
"It might seem from the outside that it's time to prove myself out of the Twilight franchise, to see if I can hold the next one up," she says. "But honestly I was so moved by this [the Snow White] world.
"It's close to my heart. It all fell off the train for me and is kind of awesome."
With Twilight, on-set incursions by fans were a nearly daily occurrence. Was it nice to get away from Bella-mania and shoot Snow White in England? "While we had a couple of visitors, it wasn't even close to [Twilight].
"Twilight is such a different thing. If there is an iconic scene, the entire crew is standing there going 'ooh, how are they going to do that?'.
"It was more of a show than a genuine experience at times."
After Snow White, she will stretch herself with edgier roles. First up is Walter Salles' adaptation of the beat classic On The Road, in which she performed her first nude scenes. "It's pretty explicit," she says.
"I got the job when I was 16. I'm happy I ended up doing it when I was 21, and not just because of the nudity aspect.
"Because I'm older it made it a lot freer for us to just completely lose control and let people watch. [While shooting the movie] I didn't really think about it.
"I'm sure I'll see it and go 'woaah!'"
So finally Stewart gets to leave Twilight behind. Will she miss Bella?
"Every project you start... you want to finish it. You want to get to the end, see how it turns out. I'm relieved on the one hand because the story is almost done.
"I was waiting for Bella's story to be fully realised. Now that it's done it's an enormous relief. But I'm not trying to distance myself from Twilight. It is something I want to keep remembering."
Snow White and the Huntsman is out today, see review page 20