Kristen Stewart packs a powerhouse performance in Spencer – Pablo Larrain’s extravagant tale based on the life of Diana Princess of Wales. But if you thought Spencer was little more than a character study of the People’s Princess, think again. Instead, Larrain has made something really special here – using smaller moments over the more well-publicised ones to build a portrait of a woman living her life publicly. Albeit in little more than a gilded cage.

The opening subtitle tells us exactly what’s in store – “A Fable from a True Tragedy”. This is not a broad biopic. Instead, Spencer tells the story of a three-day period over Christmas, ten years after Diana’s marriage to the Prince of Wales.

It’s an excellent choice. Limiting the scope of this piece to such a short time period allows Kristen Stewart much more artistic license to portray the feeling and emotion rather than historically accurate facts. And this is where Spencer really shines. Kristen Stewart offers a staggering yet subtle performance as Diana, who seems to navigate her life of royal duty from one moment to the next.

Heading to Sandringham alone in a sports car, Diana briefly pulls into a roadside diner, declaring that she’s ‘completely lost’. It’s that sense of confusion and being lost in her own life that Kristen Stewart plays with gusto – and as Diana arrives for the royal Christmas, the symbolism is layered on in heaps and spades.

Timothy Spall is wonderful, as usual, as Major Gregory – a royal equerry who has been charged with making sure Diana behaves. After all, the British press are keeping a keen eye on the princess. And the royal household doesn’t want any slip ups.

What unfolds is a three-day period of intense scrutiny and isolation – even in a roomful of people, you get the sense that Diana is completely alone. That’s partly down to Stewart’s impeccable portrayal, but also due to Larrain’s deft hand in setting up her crushing, maze-like surroundings. The royal household often feels more like the Overlook Hotel, and it’s this claustrophobic mood which only heightens Diana’s isolation. Her itinerary is meticulously planned from one moment to the next, as she navigates painfully rigid family meals and a bone-crushingly strict regimen. Even her wardrobe has already been chosen for her.

You get the sense that Diana was given no chance to breathe, let alone make her own decisions. It’s soul-crushing to watch, and Stewart often brings it all painfully to life with just a glance. Spencer really is a masterclass in understated performance, and Kristen Stewart shines – albeit subtly.

Elsewhere, Diana’s husband, the Princess of Wales (played by Jack Farthing) is as uptight as ever. Charles often receives the same treatment in the eyes of the media – painted as little more than a stuffy, unyielding man, bound by honour and duty. It’s a similar case here, but Farthing’s performance acts as a foil for Kristen Stewart’s anguish. Diana is all too aware of the Prince’s affections for Camilla Parker Bowles, and this only serves to heighten the film’s tension to inescapable levels. Despite this, there are some tender moments – largely between Diana and her sons, William and Harry (played by Jack Nielen and Freddie Spry). These moments offer some much-needed respite between the coldness of the rest of her bleak existence. And the occasional warm exchange with royal house staff shows Diana that she’s not alone.

But as the weekend continues, so too does her torment. Eventually, the cracks begin to widen, with Diana’s struggle with bulimia and self-harm laid bare. A shift in tone leads to a more gothic telling of her story as Diana reads about the equally unhappy Anne Boleyn. Forcing her to confront her own unhappiness, her thoughts take on a darker meaning, and it’s clear that she has reached a point of no return.

Of course, we know how her tragic story plays out. But the genius in Spencer is reframing it as an almost mythical tale. We confront the innermost demons of a woman whose life was barely her own. And it’s an incredibly bold choice to premiere the film so close to the 24th anniversary of Diana’s death.

Spencer is an absolute masterpiece, with incredibly close character work and a staggering performance from Kristen Stewart. Pablo Larrain traverses the royal household in a wholly new and uncomfortable way, bringing a sense of psychological terror to a story we have seen played out time and time again in the media. But this is closer, more brutal and much more raw.

Rating: ★★★★