Q: Who was Diana, Princess of Wales?
A: Diana was the ex-wife of heir to the throne the Prince of Wales, and the mother of the Duke of Cambridge and Prince Harry.
She was born the Honourable Diana Spencer on July 1 1961, third daughter of Viscount and Viscountess Althorp, and her family had close connections with the royal family.
Q: What was she famous for?
A: Her humanitarian and charity work and her compassion. Tony Blair called her the "people's Princess". She championed causes such as the fight against landmines and changed attitudes to those diagnosed with HIV and AIDS, and brought a more touchy-feely approach to the Royal Family.
She was one of the most photographed women in the world and was known for her fashion sense.
But she also hit the headlines for her troubled marriage to Charles and their subsequent divorce, her affair with cavalry officer James Hewitt and the Panorama television interview in which she laid bare many of her problems such as bulimia.
Q: When did she marry Charles?
A: Shy Lady Diana Spencer was just 20 when she wed the Prince of Wales on July 29 1981 at St Paul's Cathedral. They first met through Diana's older sister, who briefly dated Charles, and in 1980 Diana was the Prince's guest at Balmoral.
It was dubbed the fairytale wedding of the century. Diana wore a billowing Emanuel silk taffeta gown. Around 650,000 people gathered on the streets of London to catch a glimpse of the bride and groom, and 750 million across the world watched the events on TV.
Q: What went wrong?
A: When Charles and Diana's engagement was announced in February 1981, they were asked if they were in love. Diana replied "Of course", but the Prince added inauspiciously: "Whatever love is."
Before the wedding Diana became paranoid after finding a bracelet Charles had made as a present for his former lover Camilla Parker Bowles. It featured F and G for Fred and Gladys - their pet names for one another.
Q: And on the honeymoon?
A: Even on the honeymoon, all was not well. On the Royal Yacht Britannia, Diana was furious when she noticed the Prince wearing a pair of gold cufflinks engraved with interwoven Cs - a present from Camilla, and her fears grew that he was still in love with Mrs Parker Bowles.
The young Diana found she had little in common with her philosophical husband, who liked painting, reading non-fiction essays, and hunting.
Q: How did it descend into the War of the Waleses?
A: The Waleses had two children - William in 1982 and Harry in 1984 - but the cracks in their relationship were already beginning to show.
The Princess found the palace courtiers unapproachable, and was overwhelmed by her role as a royal superstar. Behind the scenes, she developed bulimia. Charles was at a loss as to how to comfort her.
In tapes recorded by a voice coach, Diana revealed when she quizzed Charles as to why Camilla was still part of his life, he told her: "I refuse to be the only Prince of Wales who never had a mistress.''
Meanwhile, Diana had an affair with cavalry officer James Hewitt.
Q: When did they separate?
A: In June 1992, Andrew Morton's book Diana: Her True Story - with which she secretly collaborated - was published, alleging the Princess was deeply unhappy and had attempted suicide.
A disastrous tour of Korea by the ill-at-ease Prince and Princess took place in November 1992. They were nicknamed The Glums and a month later it was announced they were separating.
Q: And divorce?
A: Charles confessed to an affair in an interview and book with Jonathan Dimbleby, and then Diana gave a Panorama television interview in which she said of her relationship with Charles "there were three of us in this marriage" and questioned his suitability as king.
It prompted the Queen to urge them to divorce, which they finally did in 1996. Diana was stripped of her HRH title.
Q: How did the Princess spend her final year?
A: She resigned from most of her charities and began her anti-landmine campaign, visiting mine fields in Angola and travelling to Bosnia.
Diana split from heart surgeon Hasnat Khan, whom it is claimed she had wanted to marry, and began a relationship with Dodi Fayed, son of tycoon Mohamed Al-Fayed, who at the time owned Harrods department store.
Q: How did Diana die?
A: She was killed suddenly in a car crash on August 31 1997, when she was 36 - and when William and Harry were just 15 and 12.
The Mercedes she was travelling in with Dodi was being pursued by the paparazzi after leaving the Ritz Hotel in Paris, when it crashed in the Pont de l'Alma tunnel.
Q: What about the conspiracy theories?
A: The Princess's death became the subject of many conspiracy theories, from claims by Dodi's father Mr Al-Fayed that the couple were murdered in a plot hatched by MI6 on the orders of Prince Philip, to suggestions Diana was pregnant.
Other theories centred on the lack of CCTV footage from the tunnel and the mysterious white Fiat Uno, which is said to have come into contact with the Mercedes, but which has never been traced.
Q: What did the inquest find?
A: Ten years after the crash, a high-profile £4.5 million inquest found that the Princess was unlawfully killed because driver Henri Paul was drunk and driving too fast, and the car was being chased by photographers, and that Diana and Dodi might have survived had they been wearing seatbelts.
The findings followed the Metropolitan Police's three-year Operation Paget investigation which cost £8 million and concluded it was a tragic accident.
Q: Are there still suspicions?
A: In 2013, the police explored new claims that Diana and Dodi were murdered by the SAS, but eventually said there was "no credible evidence".
Q: How did the public react to her death?
A: A sea of flowers was left at the gates of her home, Kensington Palace, by shocked members of the public and hundreds of thousands of mourners gathered in London on the day of the funeral.
Q: How did the monarchy respond?
A: Too slowly, and by misjudging the public mood.
Diana's death triggered one of the monarchy's worst crises in modern history. When the Queen remained at Balmoral to comfort her grandsons, the newspaper headlines screamed: "Show us you care" and "Where is our Queen? Where is her flag?".
The flag pole at Buckingham Palace remained bare, as was the protocol, because the Queen was away in Scotland.
The monarch, who eventually addressed the nation five days after the Princess's death, relented by flying the union flag at half mast over Buckingham Palace for the first time on the day of Diana's funeral.
Q: What happened at her funeral?
A: A young William and Harry walked behind her coffin as it proceeded through the streets on its way to Westminster Abbey.
Diana's brother Earl Spencer gave a controversial eulogy which was seen as an attack on the Royal Family.
He vowed to Diana in his speech that her ''blood family'' would do all they could to protect William and Harry ''so that their souls are not simply immersed by duty and tradition but can sing openly as you planned''.
Q: How is she being remembered for the 20th anniversary?
A: William and Harry's determination to make their mother proud has inspired much of their charity work, and they paid tribute to her warmth and humour in a recent ITV documentary where they shared family photos.
Princess Charlotte has Diana as one of her middle names, and on July 1 - Diana's birthday - the Cambridge family, Harry and the Spencers attended the re-dedication of her grave at Althorp.
A statue has been commissioned by her sons for the grounds of Kensington Palace.
Diana's candid confessions about her troubled marriage and life were also broadcast in the UK for the first time in a Channel 4 documentary using controversial video footage recorded by the Princess's voice coach.
Q: What impact is her death still having?
A: Reverberations are still being felt. Harry recently acknowledged he came close to a breakdown after not speaking about his mother's death for many years.
He also attacked the decision to make him walk behind the coffin, saying no "child should be asked to do that, under any circumstances".