Two films in the recent past succeeded in the seemingly impossible, bringing audiences vital close-ups of real-life figures whose personalities were obscured by fame, infamy and history:
Stephen Frears's The Queen allowed empathy with a monarch who for years had seemed carved in stone; Oliver Hirschbiegel's Downfall gave Germany's first portrait of Hitler, which chillingly showed that the monster was a human being after all - and therefore all the more monstrous.
If only Frears and his screenwriter Peter Morgan had returned to the Windsors and the one member of the family who did always seem accessible to us: Diana.
Instead it's Hirschbiegel, who proves he's far less adept on foreign soil.
In attempting to shed light on the real woman behind the media construct, Hirschbiegel and his writer, Stephen Jeffreys, merely threaten to break the spell Diana had over so many - not because they've revealed someone unforeseen, shocking or dislikeable, but because they make her tragic life seem indescribably trite.
They focus on the two years leading to her fatal car crash, in particular on her relationship with the Pakistani heart surgeon Dr Hasnat Khan, a love affair that reportedly came close to bringing Diana happiness. However significant its central character, the result is little more than the sort of princess and commoner love story that would usually service a cheesy romcom.
We first see Diana (Naomi Watts) alone and lonely in Kensington Palace, rehearsing for the impending Panorama interview that would bar her irrefutably from the throne. Separated from Charles and kept at arm's length from her sons, she is struggling for a sense of purpose. The incendiary interview is about to throw her into the unknown; all she needs is someone to catch her.
A chance meeting with the surgeon (Naveen Andrews) provides just the man. The princess is struck by the doc's initial indifference - a shock for the self-appointed "Queen of people's hearts", but in keeping with Khan's single-minded personality and unbending attention to his work. That said, when she coquettishly pursues him, he responds.
What ensues seems like a courtship from another planet. Surprisingly, given his profession, Khan lives on a diet of junk food and cigarettes, and spends his first date with Diana munching on Burger King in front of Match Of The Day. He also gets the worst of the script's many appalling lines. "You don't perform the operation," he comments sagely.
"The operation performs you."
All this, even his drab digs (there's no explanation why a London heart surgeon lives in a bedsit), bewitches the young princess, who regresses into a state of simpering adolescence. The film's point is that the poor thing had never experienced such sincere regard; loved by all, accepted by no-one, she complains, a sad scenario that will be maintained as the very private Khan is eventually repulsed by the media spotlight. Yet this observation is hardly insightful.
Jeffreys also argues that Khan's influence led to Diana's most memorable role, as a campaigner, notably against landmines. But if the intention is to affirm the caring young woman of the public's fond memory, it's undone by the spurious suggestion that Diana only embarked on her affair with Dodi Fayed in order to make Khan jealous. A petty act if true, it muddies rather than sparks a banal piece of storytelling.
Watts captures Diana's sensuousness, as well as the savvy and silly sides to this contradictory woman. But she's undone by a script that constantly reminds us that she's playing "the most famous woman in the world", one whose fame came for all the wrong reasons.