LONDON - Candles and flowers have been accumulating at the gates of Princess Diana's former London residence to mark 20 years since her death, which unleashed an unprecedented outpouring of grief in Britain.

"She was this ray of light in a fairly gray world," Prince William said of his mother, Diana, princess of Wales, whose death two decades ago on Thursday shocked the world.

"I still feel that love, I still feel that warmth 20 years on," her elder son said in a new documentary marking the anniversary. "If I can be even a fraction of what she was, I'll be proud."