David Miliband revealed a family connection to Anne Frank in an emotional speech to the Holocaust Memorial Day lunch of the anti-prejudice organisation set up in her name.
The former foreign secretary told Anne Frank Trust supporters that his aunt had met Otto Frank, Anne's father, in the early 1950s.
He had recently spoken to his aunt, who "had a lovely lilt when she talked about this kindly, extraordinary man who came into her life to talk about his daughter".
Praising the trust's achievements in his South Shields constituency, Mr Miliband said he had another reason for wanting to honour the teenage diarist's memory.
"My mum and her sisters and my father's sister spent the war in hiding like Anne Frank. Their lives would have been ordinary but they were wrenched from normal life to fight for survival. Thanks to the extraordinary bravery of people, they were survivors."
It had been 70 years since Anne received "her precious blank diary" and with the Holocaust "receding from memory into history", the power of Anne's words was even more precious.
"Her diary speaks across generations. One of the things I like about it is that the trust uses her memory to try and bend the arc of history. This is a trust which is committed to honouring the past and learning from it to shape the future. There are many, many Anne Franks who are fighting for their lives around the world."
He added that the diary raised the question of "whose responsibility it is to fight cruelty," citing conflicts in Syria as an example of how this question continued to be relevant.
The 500-strong turnout at the Park Lane Hilton included Stephen Lawrence's mother, Doreen, and Margaret Mizen, whose teenage son was also murdered. Holocaust survivor Renee Salt and Sudanese human-rights campaigner Kamal Kambai were among other guests.
Former Sun editor Kelvin McKenzie, who was on the lunch committee, said that if the trust could have reached more people, "perhaps Stephen Lawrence and Jimmy Mizen wouldn't have died as teenagers".
Knowing Anne Frank's story, "you would literally be stupid to judge anyone by their race or colour. Let's try and create a generation of adults who are prepared to challenge bigotry and hatred with a sense of compassion."
Trust executive director Gillian Walnes said what happened at Auschwitz would "forever scar the human race". The trust hoped "to take the lessons from the past into the present day to show how prejudice and brutality can harm".
The impact of its work was highlighted by Callum McKean, an Anne Frank ambassador from Mr Miliband's constituency, who has spread Anne's message to local schools and youth groups. "It's absolutely changed my life," he said.
The lunch raised more than £275,000 for the trust's work in challenging prejudice and hatred.