One of the most famous women in the world, Diana was killed aged 36 on Aug 31, 1997, when her limousine crashed in a tunnel as it sped away from paparazzi giving chase on motorbikes.
Her death prompted the biggest outpouring of grief seen in Britain in recent times and hurt the monarchy, which was accused of reacting coldly.
The events that followed, when Queen Elizabeth promised to learn from Diana's life, are regarded as a turning point in the modernisation of the country and how the royal family relates to the public.
"The royal family can be a bit cold, and she was warm hearted and kind. She was very special and we want to keep her memory alive."
On Thursday, fans gathered in the dark to lay candles and remember a woman who married Prince Charles, the heir to the throne, in a glittering 1981 wedding ceremony before their bitter divorce in 1996.
The 20th anniversary of Diana's death has prompted a renewed fascination with the "People's Princess", as she was dubbed by then-Prime Minister Tony Blair, with her two sons Prince William and Harry leading the tributes.
In documentaries broadcast in recent weeks, the two men have spoken about the trauma they suffered from their mother's death and their sense of confusion and bewilderment at the country's grief.
"Their courage to be openly vulnerable and to talk about these issues is a mark of how the royal family has changed and an example of the role a modern royal family can play in British life," it said in an editorial.
"The princes have led the way in dispensing with the stiff upper lip against which Diana railed."