Chris Imafidon, chairman of the Excellence in Education Programme, said Princess Diana touched the lives of everyone she met, including many of the programme's students.
The award-wining non-profit works with schools, local groups, companies and charities interested in the educational development of students in inner-cities and children from socially disadvantaged backgrounds.
“Kensington Palace, during her time, used to have a lot of our students come here to the garden for an ice cream party in the summer,” Prof Imafidon, who wrote the 2016 book 90 Things you Didn’t Know about Queen Elizabeth II, told The National. “And she used to come around and speak to different children from low social economic backgrounds, inner city kids.
“She would sit down, look them straight in the eye and say what do you want to be when you grow up? And she would turn round and say yes, you can. Those children went back to school and they did things differently. When the teacher asked why? They said 'even the princess said I can be this. I can do this'.”
That inspired many girls to pursue careers in STEM ― science, technology, engineering and mathematics, he said.
He also spoke about when Princess Diana visited Aids and HIV patients, many of whom did not even receive visits from their families because they were frightened of catching the virus.
“The minister said don’t go there. You are not supposed to go there,” he said.
“If you go there you will catch Aids. Guess what, she said no, she must go there. And she shook hands with them, with her fingers, no gloves, she sat on their beds.”
She made everyone think and believe they were important, he said.
“She believed everybody was important and she liked unifying people.
“She told Nelson Mandela, 'go and invite FW de Klerk', a white South African leader, 'for dinner so the two of you can unite to build South Africa'.
“'Because if you keep fighting and saying he was bad to me and he was nasty to me, South Africa will not progress.' This is something that most people don’t know.
“And Desmond Tutu said it when Meghan and Harry went to visit him. He said 'look, your mother did this and this and this and Harry was crying'. Because nobody told them,” he said.
She was more than the Princess of Wales, Prof Imafidon said.
“She was not princess of Europe. She was princess of the world.
“She showed equity, uniformity and love that the world needs today.”
The princess was just 36 when the limousine carrying her and her partner Dodi al-Fayed crashed as it sped away from photographers who were chasing it on motorbikes.
Prof Imafidon was among dozens of mourners who visited Kensington Palace on Wednesday to pay tribute to the princess. Many laid flowers.
"Instead of being 25 years it's like yesterday. It transports you right back to those days," said Jane Crook, 64, a school worker from Wales.
Morgan Hindle, 23, a support worker from Manchester, said: "She was such an amazing person and an icon and I think she meant so much to so many people ... I think she's someone who needs to be remembered for ever."
Every year tributes left outside Kensington Palace recall the mountains of flowers piled there in the days after Diana's death.
The accident that led to her death shocked a generation. It also capped life lived in the intense glare of the media. Diana's fairytale wedding, ugly divorce and efforts to build a new life all made headlines.
The public watched as she blossomed from a shy teenager into an international style icon who befriended AIDS patients, charmed Nelson Mandela and walked through a minefield to promote the drive to eradicate landmines. Along the way, she showed the royal family, particularly her sons William and Harry, how to connect with people and be relevant in the 21st century.
Maria Scott, 51, paid her respects to Diana as dawn broke over the palace, just as she does every year.
“There was just something about that girl that really stood out. And of course, I watched the wedding, the fairy-tale princess,’’ Ms Scott said. “And, you know, you see, she was like part of your life because you were seeing that every day on the television. She was in newspapers, magazines. She was all over. And you felt like she was part of your life.”