Either way, the response showed just how much Diana’s journey from shy nursery-school teacher to People’s Princess appears burned into the collective psyche.

This renewed interest in Diana may simply be down to timing. Next year marks the 25th anniversary of her death, and – movies aside – you can expect a wealth of coverage to mark the occasion.

Diana was a figure ingrained in popular culture when she was alive, and even more so in death. In 1993, four years before she was killed in a road accident in Paris, the made-for-TV movie Diana: Her True Story was released, cynically cashing in on the fact Charles and Diana had separated a year earlier.

Adapted from Andrew Morton’s 1992 revelatory biography of the same title, it steered audiences through Diana’s loveless marriage with Charles, touching on her eating disorders and his love for Camilla Parker-Bowles.

Starring Serena Scott Thomas (young sister to fellow actress Kristin) as Diana, it even went as far as dramatising one of Morton’s juicier titbits – that Diana, pregnant with her first child, threw herself down the stairs after an argument with Charles.

At the time, there were other TV movies too, such as American network ABC’s Charles and Diana: Unhappily Ever After. After her death in 1997, when her car spun out of control in a Paris underpass while being pursued by paparazzi, the film and television industry wisely took a step back.

When her death was approached as a subject, it was done with huge sensitivity – notably in 2006’s The Queen, written by The Crown’s creator Peter Morgan and set in the days after the tragedy.

Now she appears fair game once again for filmmakers. In the case of Spencer, the movie will not focus on her death. It is set in 1992 at the Sandringham royal estate, when, in the three days over Christmas, a lonely Diana tells Queen Elizabeth that she wants a divorce from Charles. As Stewart recently stated: “Spencer is a dive inside an emotional imagining of who Diana was at a pivotal turning point in her life.”

With a script from British-born Steven Knight (creator of the hugely popular BBC show Peaky Blinders), the most intriguing aspect of Spencer is the choice of director: Pablo Larraín. The Chilean filmmaker already has form in this arena, after his Oscar-nominated 2016 film Jackie .

That film convincingly dipped into the traumatised and fragile mental state of Jacqueline Kennedy, as played by Natalie Portman, in the horrifying aftermath of the assassination of her husband, US President John F. Kennedy.

As for non-fiction accounts, there are already dozens of Diana documentaries and podcasts. Among them are National Geographic’s Diana: In Her Own Words, taken from audio interviews between Diana and Andrew Morton, and the BBC’s Diana, 7 Days That Shook the Windsors, which, like The Queen, dealt with the immediate fallout from Diana’s death.

When Prince Charles and Princess Diana visited Hong Kong

While these were always destined for television, there is now a documentary with an intended theatrical release in the works.

Simply called Diana, it’s due for release in 2022. Directed by Ed Perkins, an Oscar nominee (for his short Black Sheep), this will be the first Diana doc to make it into cinemas and will see Perkins dive into the wealth of archive footage available – no mean feat given Diana was one of the most filmed people on the planet.

“The idea of taking an archive-only approach will allow us to immerse audiences in the narrative as if it were being told in the present,” Perkins has promised.

Yet if there’s a warning bell for filmmakers approaching the subject, it’s 2013’s Diana, starring Naomi Watts in the title role. Based on Kate Snell’s 2001 book Diana: Her Last Love, it focused on the last two years in the subject’s life, specifically her relationship with British-Pakistani heart surgeon Hasnat Khan (played by Lost’s Naveen Andrews).

The film clearly had the best intentions, with Watts repeatedly watching Diana’s notorious 1995 interview with BBC show Panorama when she spilled her guts to journalist Martin Bashir.

As with Spencer, the film’s producers took the decision to hire an outsider as director: German-born Oliver Hirschbiegel, whose 2004 film Downfall (about the last days of Adolf Hitler) had been nominated for an Oscar. Unfortunately, the result was anything but award-worthy.

“It has the slightness of a Barbara Cartland novella, but the love affair is treated with ponderous solemnity, as though it were another Gone with the Wind,” opined the Daily Mail, the mid-market British tabloid that’s practically made a cottage industry out of peddling Diana stories to its readers.

“The English gave me quite a bashing for the film,” Hirschbiegel told this writer, “and it’s a beautiful film. It’s a beautiful love story.

“They just didn’t want that kind of story about their Princess Diana. They didn’t really want to know anything about Princess Diana at the time, as it turns out! And the Germans liked the film!”

The film ultimately grossed US$21 million around the world, despite its fairy tale Mills and Boon qualities. “I would’ve done the very same [if I’d made it again],” says an unrepentant Hirschbiegel.

While Spencer will be first out the gate, it will coincide with the filming of the fifth season of The Crown – with the elegant Australian star Elizabeth Debicki ( Tenet ) taking over from Emma Corrin as Diana as the story picks up in 1990 – and will inevitably include her death.

With the that season of The Crown likely to be screened in the autumn of 2022, a quarter-of-a-century after Diana’s death, it would be nice to think that filmmakers could call time on Diana documentaries and feature films after this.

Somehow, though, that seems unlikely.

The Crown is available on Netflix. Spencer will be released later in the year.

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