Actors are often sentimental, emotional, and gushing when they have the chance to discuss their role.

But in the case of Kristen Stewart, who took on the challenging task of playing Diana, Princess of Wales, in the film Spencer — which opened amid great fanfare on Friday — something unusual happened.

Twilight’s star actress, and also the star of Twilight, was not speaking of her but the character she played.

In a moment of personal modesty, she demonstrated a rare insight — possibly gained from her own experience of fame — into Diana’s troubled role as the most famous (and most photographed) woman on the planet.

‘It’s feeling constantly watched, no matter what you do,’ she says. ‘If you’re in public, someone in the room is looking at you at all times.

‘Even if they’re not, it’s at the back of your mind. That is a feeling you only have if you’re extremely famous. It’s a completely different approach from being a human.’

Just like The Crown, with its insistence that it made scrupulous efforts to get the details right, new Diana biopic Spencer, starring Kristen Stewart, hides behind a veneer of authenticity

Like The Crown with its insistent that every detail was correct, the new Diana biopic Spencer starring Kristen Stewart hides behind an authentic veneer.

All the same, at 5ft5 in, the Los Angeles-born Ms Stewart is an unlikely choice to take on the persona of the aristocratic princess (pictured on Christmas Day at Sandringham in 1993)

Ms Stewart was 5ft5 inches tall and is a unlikely candidate to play the role as the princess aristocratic (pictured at Sandringham on Christmas Day 1993).

This was an extraordinary observation by someone, who was seven years old when Diana died in the Paris underpass car accident. It may have even been made by Princess Diana herself.

The 5ft5in, which is a little less than Diana’s height, makes Ms Stewart a very unlikely candidate to assume the role of an aristocratic princess.

While she has some elements of Diana’s style, her fragility and humor, there is no trace of Diana’s grace or sense of humor.

Ms Stewart’s voice is too soft, her head tilted too often, leaving only the wardrobe to convince. Though, as she herself has said, lamenting her own lack of stature: ‘I am playing Diana. I’m not her.’

Some critics have marvelled at Ms Stewart’s portrayal and have installed her as a favourite for an Oscar in March, but will audiences warm to her and leave cinemas feeling that they understand Diana as they never did before?

They will not be allowed to do so, as the movie’s satire of the princess’s batty behavior and the indifference displayed by the royals is completely untrue.

Spencer is just like The Crown with its insistent that every detail was correct, but he hides behind an appearance of authenticity.

This isn’t the only thing it shares with Netflix. Members of the Royal Family are shown as haughty and cruel while enveloped by protocols so rigid that they would be laughable if they weren’t so lamentably absurd.

Unlike in the latest film about her life (pictured), Princess Diana never drove a Porsche

Princess Diana did not drive a Porsche, unlike the film that depicts her life.

The movie purports to cover the three days of the Christmas gathering at Sandringham in 1991, when — it claims — the princess took the decision to end her marriage. The movie is fiction.

The marriage did not formally end for another year — why didn’t they choose December 1992 instead? — and actually the inevitability of her separation from Prince Charles dates back to at least six months earlier.

Even though the picture opens with the message on screen: ‘A fable from a true tragedy’, the filmmakers are hoping to pull the same stunt as The Crown by boasting of their precision in the details.

Scriptwriter Steven Knight — creator of TV’s Peaky Blinders — says his descriptions of the bizarre Christmas rituals included in the film are word-of-mouth details from people who worked at Sandringham. ‘All the things in the film that seem least believable, are true,’ he insists.

Is that really true? This presumably includes the practice of members of the Royal Family sitting down on an old-fashioned weighing machine on their arrival and again on departure — because the Queen likes everyone to put on three pounds over the festive period.

This myth is completely false. It is true that there was once upon a time a sit-on scale, a museum piece tucked away near Sandringham’s main entrance, but it had not been used for more than a century.

‘It was last working in the reign of Edward VII,’ says a former Sandringham servant. Doubtless, many will choose to believe this portrait of a princess trapped in an unhappy marriage surrounded by the brutish hostility of her husband’s family.

But the film’s credibility is stretched from the very beginning — an opening sequence which has the princess driving alone to the royal residence behind the wheel of a Porsche and inexplicably getting lost in the Norfolk backroads.

The pearl necklace Diana feels is strangling her is just one of the symbolic tools used in the film

Just one symbol used by the film is Diana’s pearl necklace, which she feels strangling.

It is absurd. Diana was born in Norfolk, and she spent her first 14 years in Park House. This is part of Sandringham.

What about driving on your own? Were her police officers bodyguards there? The Porsche was never in her possession.

However, losing her way did allow director Pablo Larrain to insert one of his many symbolic devices: the princess stops at a café to ask directions. What is its name? The Duch, the nickname Diana’s Spencer siblings gave her as a child because she acted like a duchess.

So what really went on at Sandringham that Christmas almost 30 years ago — and what was the state of the royal marriage? Importantly, what was the point of her divorce?

The abiding memory of that year’s Christmas was the freezing fog that blanketed north Norfolk over the holiday.

While the princess did not drive alone, she was driven to Kensington Palace by William, 9, and Harry (7), who arrived on Christmas Eve. Yes, there were police officers who accompanied the celebration.

Instead of the three days she was supposed to be there, the Princess stayed for over a week.

Prince Charles traveled from Highgrove where he’d been living for several months.

Diana, Princess of Wales on a visit to Portsmouth, on January 23, 1989 in Portsmouth

Kristen when playing Diana, pictured

Kristen Stewart, pictured as Diana, left, has stated that the fame and popularity she has received has helped her understand the pressure Diana (pictured right in 1989) felt when she was preparing for her role in Spencer

Although they were never in complete separation, their only contact was with the children and official engagements.

In fact, the marriage had reached a psychological tipping point months earlier, with the removal in May of the prince’s then-private secretary Major General Sir Christopher Airy.

Diana loved the Guards officer of the past and after his departure the office that served both prince and princess was split effectively.

Nothing illustrated that more than the aftermath of Prince William’s accident that summer, when he had been unintentionally struck on the head with a golf club.

He was rushed by his parents to hospital where he received surgery for his skull fracture.

While Diana was still at the hospital’s bedside, Charles went to the Royal Opera House for an official engagement.

Media coverage of the prince’s absence was savage, fuelled by the briefings from now rival royal teams.

After Diana offered help to someone who fell at the royal events, the prince laughingly accuses his wife.

Matters reached a head when reports that the princess had turned down her husband’s offer of a 30th birthday party in July were leaked to the Daily Mail.

Diana did not think an extravagant ball would impress the public and she had no wish to share her big day with many of her husband’s Highgrove cronies.

The publicity caused some reorientation. During the summer, there was a family cruise with William and Harry, and on Charles’s birthday in November, Diana accompanied him to see Oscar Wilde’s A Woman Of No Importance at the Barbican in London.

She scored a spectacular success with her first solo foreign tour to Pakistan and she and Charles managed to put on a united front for a visit to Canada, long remembered for a memorable picture of William and Harry racing into their mother’s arms on the deck of the Royal Yacht Britannia.

The following month Diana was on the cover of December’s Vogue magazine, suffered a bout of flu and was praised for making an official trip to Ulster’s ‘bandit country’ at a time of heightened IRA activity.

She was happier than she had been at Christmas before and went to Sandringham feeling more relaxed.

There were 18 members of the Royal Family at the Norfolk mansion that year, including Prince Andrew and the Duchess of York, whose marriage was much closer to collapse than the princess’s.

Other royals are barely mentioned in the movie, except for the Queen and Charles.

Kristen (pictured) said her favourite scenes to shoot involved Diana losing herself in dancing

Kristen (pictured) stated that Diana’s dancing is one of her most favorite scenes. 

In fact, Diana spent much of the holiday with Fergie as the two women became regular visitors to the Knights Hill health club in nearby King’s Lynn, where they swam with Harry and three-year-old Beatrice and also used the spa.

There was one other significant — and highly secret — activity going on at this time in the life of the princess: her collaboration with the writer Andrew Morton.

Throughout 1991, Morton had begun compiling material for his best-selling book about Diana’s marriage, including cassette tapes on which she had secretly recorded answers to his questions.

The book had reached a crucial stage by the Christmas holidays. To make sure she was able to go over the chapters and offer suggestions and marks, she even traveled with several completed chapters.

Her main concern was the title. It should be called Diana, The True Story. Morton, his publisher and she suggested Diana, Her True Story.

‘There was a lot of back and forth over the title,’ Morton recalls. ‘We sent mocked-up book jackets for her to look at and she eventually came round to our point of view.’

It was the publication of the devastating biography the following June, with its searing revelations about the prince’s love for Camilla Parker Bowles and Diana’s suicide attempts, that was to fatally undermine the royal marriage. But, in Spencer, it doesn’t rate so much as a mention.

The film also suggests that Diana was given Queen Victoria’s room that Christmas. However, this was false.

Although the prince and princess no longer shared a bed — and hadn’t since 1987 — the couple did occupy a suite at the top of Sandringham House known as the nursery floor.

Diana was the queen and Harry slept next to Harry in the dressing room.

Of course it was a ruse and the princess and prince were barely speaking. The mood was hardly improved by media interpretations of the Queen’s broadcast, which the family all watched together on Christmas afternoon.

In it, the Queen spoke of her intention to serve the nation — and the Commonwealth — for ‘some years to come’.

It was interpreted as a monarch ruling out the abdication of her throne and vowing to keep the vows made almost forty years ago as a young queen.

Diana claims that Prince Charles did it and that he blamed Diana for the situation in their marriage.

We see Kristen Stewart run towards the flashing guns in Spencer’s most bizarre episode.

That was only one ridiculous thing about the shooting. Although Diana was not a fan of bloodsports, it’s true that Diana would question a chef about the fates of the shot pheasants.

Her family was raised on Althorp Estate, which had its own shooting. It was there that she met Prince Charles.

In fact, in 1991, she joined the Queen, Prince Edward, Philip and Viscount Linley and the other guns for a lunch at nearby Flitcham Hill in a log cabin that was a present from staff for Her Majesty’s Silver Jubilee. In winter, royal shoot lunches must be eaten indoors by log fires and not like Spencer’s picnics.

For years, Diana kept a photograph of herself at a shoot standing between her butler Paul Burrell and footman George Smith, a former Falklands War veteran who later claimed he had been raped by a member of Prince Charles’s staff.

Sadly, Spencer is littered with deliberate or accidental errors — I could supply a list.

Take the formality of the screen Diana’s relationship with the Queen. She refers to her as ‘Your Majesty’. Yet in all their private encounters, the princess unfailingly called her mother-in-law ‘Mama’.

Almost every scene in this joyless film is drenched in symbolism — from the pearl necklace Diana feels is strangling her, to the mountains of food prepared in the Sandringham kitchens and its references to the princess’s bulimia.

It is true that Diana did not decide to end their marriage at Christmas 1991. The facts are irrelevant: why should they get in between a great story and the truth?