The late Diana, Princess of Wales, was a trailblazer, a style icon and one of the most influential women of the 20th century.

But, by all accounts, once she stepped onto the stage of public life in 1980, self-preservation meant she lived in two separate worlds – one personality confidently in the spotlight as the adored People’s Princess.

In her private life, Princess Diana was a more oppressed, scrutinised member of the royal family who struggled with insecurity and loneliness.

And never the twain shall meet.

As the thousands of newspaper articles tracked her every move when she joined the royal household in 1981, books and essays revealed her inner turmoils and conflicts and documentaries spun various visual angles of her trajectory up to her death.

Possibly the most heartbreaking chapter of her life was just before she died.

Diana, Princess Of Wales is seen in St Tropez in that fateful summer of 1997. Photo: Getty

The real private life of Princess Diana

She called her butler Paul Burrell in a marathon 40-minute phone call from her then boyfriend’s yacht, the Jonikal, floating in the Mediterranean.

It was in the 24 hours before she was killed in the Pont de l’Alma tunnel in Paris. We only saw the paparazzi photos of her, looking slim and suntanned in designer one-piece swimsuits.

But in that candid chat she revealed so much more.

Recently completed ITV documentary Diana, aims to tell “the definitive story of the most famous woman in the world” to mark what would have been her 60th birthday on July 1.

Executive producer David Glover says “her 60th birthday feels like the perfect time to re-examine her life and legacy and explore just how she went from a relatively unknown teenager to the most-mourned person who ever lived”.

However, there were only a handful of people who could really lay claim to knowing the real princess behind closed doors.

Paul Burrell (in white shirt) in Bosnia-Herzegovina as part of her campaign to raise awareness about landmines on August 10,1997, 21 days before she died. Photo: Getty

‘The only man I trust’

Mr Burrell, Diana’s “most intimate confidante” continues to talk publicly about royal matters to this day, and has been described over the years as Diana’s “rock”.

Diana said he was “the only man I trust”.

Mr Burrell was first seconded to Charles and Diana at their country residence, Highgrove.

After they separated in 1992, Diana requested he continue in her service at Kensington Palace. Out of everyone who worked with her, he remained by her side right up until she died.

In his widely acclaimed memoir A Royal Duty, Mr Burrell wrote about the last month of his 10-year professional relationship with her, supporting her and either meeting or talking to her daily.

In the last week of August 1997, Diana was leaving Kensington Palace to spend time on a yacht with Dodi Fayed, moored off Italy.

Mr Burrell had helped her prepare for her European vacation, buying books on spirituality, healing and psychology.

“Light reading,” she quipped.

She had also been flicking through magazines, looking at properties to buy in the US, finding Julie Andrews’ Californian clifftop mansion was up for sale. She was planning for the future.

He wrote: “As we knelt on the sitting-room floor, she pointed at the Julie Andrews property … ‘This is the main reception area. This is where William’s room will be, and Harry’s. And that annexe is where you will live with Maria and the boys [Burrell’s family]. This can be a new life. Isn’t it exciting? It is a land where anyone can achieve,’ she said.”

He also admitted he knew Fayed “wasn’t right for her”, but as he watched her skip down the stairs after tidying her office, checking she had her “passport, phone, Walkman”, he recounts: “I was leaning on the wooden bannister, looking up at her. She was wearing a simple Versace shift dress. ‘Do you know,’ I said. ‘I’ve never seen you looking so good. You look perfect’.”

He walked her outside to a waiting BMW, stretched a seatbelt across her shoulder and promised to call her.

Her final moments on British soil.

Princess Diana cut a lone figure on the Jonikal in Portofino, Italy in August 1997.

Mr Burrell spoke to her on that yacht before she went to Paris, where she revealed intimate details about fears Fayed was going to propose.

If a ring was presented, “put it on the fourth finger right hand … a friendship ring”, he advised.

She was relieved she had options.

He could tell she felt trapped and wanted to come home to England to be with her boys as he suggested he was “controlling her every move”.

Right again, she said.

Diana made him promise he would be there for her when she came home.

The happiest days were those spent with William and Harry. Photo: Getty

Two sides to a coin

In American author and historian Sally Bedell Smith’s “earnest” account of Diana’s life in Diana in Search of Herself: Portrait of a Troubled Princess, she dissects the princess from young girl to her troubled relationship with the monarchy and the press, through to her death.

Smith breaks down into minute detail what made Princess Diana tick in her private life, describing her charisma and lack of arrogance in her personal life, and how that transcended into public life.

At many points throughout her adulterous marriage, coupled with a love-hate relationship with the unrelenting British press, she struggled with bulimia, sought solace with psychics and was often alone. A dangerous combination.

Interior designer Nicholas Haslam, a friend for several years who adored her, told Smith: “The time spent alone reviewing every situation and having no friends was for planning and plotting.”

In public, there was little evidence of her “emotional storms”. Adds Haslam, who described her nature as “fresh and spontaneous”: “She could appear to be talking about something to anyone. She was a conversational chameleon.”

But Smith wrote: “Diana would dwell on her perceived inadequacies, ponder the betrayals of her past and present, and think obsessively about her enemies, both real and imagined. Her thoughts would plunge her into tears and sometimes vengeful schemes.”

On the other hand, her friends said she could step down and make other people feel really good about themselves.

“I am much closer to people at the bottom than to people at the top,” she told Le Monde in the last interview before her death, as Smith recounted.

The night Diana, Princess of Wales, died in a car crash in Paris. Photo: Getty

Richard Kay, a long-time royal Daily Mail reporter and friend of the princess, spoke to Diana in what turned out to be her last telephone conversation before she died on August 31.

“She was desperate to try and make a fresh start and do something different,” Kay told People on June 18.

“[She wanted] to explore a different kind of royalty.”

It seems she succeeded. As People wrote: “What Diana would tragically never come to realise, in fact, was that even in death she would reshape the monarchy, setting off ripples through her legacy, her love for her children and her compassion.”