Senior royals, faith and political leaders are gathering in Westminster to commemorate International Holocaust Memorial Day.
The Duke and Duchess of Cambridge are joining Prime Minister Boris Johnson at the event, which comes 75 years after Auschwitz was liberated.
The duke will give a reading and the couple will meet survivors of the Holocaust and more recent genocides.
It comes as dozens of world leaders gather at Auschwitz in Poland.
They join around 200 Holocaust survivors – including some who are now living in the UK – who have returned to the former Nazi death camp for a commemoration.
Batsheva Dagan, who was given the number 45054 on arrival at Auschwitz, told those gathered in Poland that “human dignity did not belong” at the camp.
“Quite the opposite,” she said. “Human dignity was trampled.”
In Westminster, faith leaders in attendance include the Archbishop of Canterbury Justin Welby and the Chief Rabbi Ephraim Mirvis.
Meanwhile, the prime minister has said he “will never allow this country to forget” the genocide as it was announced the government would donate £1m toward the preservation of Auschwitz.
In an opinion piece published by Jewish News, Mr Johnson also lent his support to the proposed National Holocaust Memorial and Education Centre near Parliament.
“Because even though the Shoah was a crime so unprecedented it required the creation of a new word – genocide – simply to describe it, its perpetrators wished for it to be left unnoticed by the history books,” he wrote.
Mr Johnson also denounced “a growing number of anti-Semites” who seek to cover up the Holocaust, also known as the Shoah, in which millions of Jewish people were killed.
“They downplay the scale of the killing, draw false equivalence with the contemporary world, even outright deny that what happened, happened,” he wrote. “We cannot let them gain a foothold.”
“We owe those incredible survivors nothing less,” he added.
The UK commemoration in Westminster honours survivors of the Holocaust, Nazi persecution, and the genocides which followed in Cambodia, Rwanda, Bosnia and Darfur, according to organisers.
Around one million people – many of them Jewish – were killed at Auschwitz before it was liberated by the Russian army on 27 January 1945.
The Duchess of Cambridge captured portraits of two Holocaust survivors for an upcoming exhibition and released to mark the anniversary of the liberation of Auschwitz.
One of Catherine’s portraits was of 84-year-old Steven Frank, originally from Amsterdam, who survived multiple concentration camps as a child.
He is pictured alongside his granddaughters Maggie and Trixie Fleet, aged 15 and 13.
The duchess’ other portrait is of 82-year-old Yvonne Bernstein, originally from Germany, who was a hidden child in France throughout most of the Holocaust.
She is pictured with her granddaughter Chloe Wright, aged 11.
The UK Holocaust Memorial Day commemorative event will air on BBC Two at 7pm and will be available on the BBC iPlayer.