Catholic school pupils listened in astonishment as a survivor of Auschwitz, Buchenwald and Belsen recalled how her sister was made to dig her own grave before Nazi guards shot her dead.
Gina Turgel was addressing an HMD commemoration at La Sainte Union in Camden, having accompanied Chief Rabbi Ephraim Mirvis, who spoke about the 70th anniversary of the liberation of Auschwitz. Mrs Turgel married one of her liberators, British soldier Norman Turgel.
"Still, I feel a chill on my right arm where she used to sleep on me," Mrs Turgel said of her sister. "We were told to collect wood to burn the bodies. Can you imagine having to do that task knowing what it was going to be used for?
"Young people of today have got to know they should never forget our stories, for their own sake and everybody's sake."
Among her rapt audience, Amari Edwards, 14, said: "I've heard about the Holocaust before but I've never heard it spoken about like that. It was amazing to hear that after all that horror, she found love."
Year 10 pupil Leslie Anne Simons said: "It has really changed my views about what had happened. The things I had heard about the Holocaust were 'it wasn't that bad', but this makes you understand."
Millie Kersey was one of two LSU pupils chosen to join the Holocaust Educational Trust's Lessons from Auschwitz project last year.
"I went with 200 people and the whole time not one person spoke. It was very sombre, even on the way home. I feel as a school ambassador, I've got the responsibility to share that experience and help educate about it."
Fellow HET ambassador Ellen Cusack said that hearing Mrs Turgel's story, "I could picture her right there, where we stood. Now she is here in our school telling us about it, free.
"It is unimaginable and has taught me such valuable lessons. I don't think I could have learnt that from school."
Rabbi Mirvis said: "As time goes on, Holocaust denial is likely to become a stronger, more prevalent feature within our society. So for the rest of your lives you must carry this assembly with you. Tell the stories and spread the message of the sadness of the past and the promise of the future."