Diana was 36-years-old when she killed in a car crash in Paris and left behind her young sons William and Harry.
Prince William and Prince Harry paid tribute to their mother, visiting the floral tributes at the gates of her former home Kensington Palace.
When the world reacted to the news 20 years ago, the Salvation Army decided to provide tea to those who had come to the Mall to grieve.
Major Mark Rose from The Salvation Army spoke to that crowd in 1997. He told Premier because it was major event; he felt he needed to be there.
He said: "I remember myself and my wife chatting to each other and slowly seeing the crowds gather at the palace.
"I remember saying I think we should be there; the Salvation Army should be there with the people... it's kind of part of our calling I think."
He said the Salvation Army staff responded to massive crowds and served around 300 hot drinks an hour.
He added that he was surprised by the sense of reverence for the late princess and likened it to be being in a church.
Major Rose said: "Through the ministry I found that in those moments that's when people are most aware of the whole spiritual dimension.
"When there is a sense of loss and grief, people are so much more open to talk about spiritual matters."
Listen to Major Rose speaking with Premier's Cara Bentley here:
