The King joined foreign monarchs, including Denmark's King Frederik and Spain's King Felipe, to pay tribute to Holocaust survivors at an anniversary service in Poland.
Heads of state and world leaders gathered at the former Nazi death camp Auschwitz-Birkenau to mark 80 years since its liberation.
Charles, 76, has become the first British head of state to visit Auschwitz, with the monarch telling guests at a recent Buckingham Palace reception: "I feel I must go for the 80th anniversary, (it's) so important."
Those paying tribute in Poland included France's President Emmanuel Macron, German Chancellor Olaf Scholz, King Willem-Alexander and Queen Maxima of the Netherlands, Spain's King Felipe and Queen Letizia, and Denmark's King Frederik and Queen Mary.
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© Alamy Stock PhotoDutch royals
The King was pictured arriving to take his seat at the service alongside King Willem-Alexander and Queen Maxima of The Netherlands.
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© Alamy Stock PhotoStories from survivors
During the moving service, Holocaust survivors placed a light in front of a freight train carriage – a symbol of the event – and the King with other heads of state and Government laid lights in memory of those who died.
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© Alamy Stock PhotoMoving service
Belgium's Queen Mathilde was visibly moved during the service and was seen wiping away tears as guests listened to the moving stories from Holocaust survivors.
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© Alamy Stock PhotoSpanish royals
King Felipe and Queen Letizia listened intently to Holocaust survivor Janina Jwanska.
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© Alamy Stock PhotoNever forget
Earlier in the day, Charles said the testimony of Holocaust survivors teaches us to "never be a bystander in the face of violence and hate" as he visited the Jewish Community Centre (JCC) in Krakow.
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© Shutterstock/POOL/AFP via GettyThe King's speech at the Jewish Community Centre
In his speech, His Majesty added: "As the number of Holocaust survivors regrettably diminishes with the passage of time, the responsibility of remembrance rests far heavier on our shoulders, and on those of generations yet unborn.
"The act of remembering the evils of the past remains a vital task and in so doing, we inform our present and shape our future."
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© GettyPlacing candles
After the Holocaust survivors placed their candles on the carriage, world leaders and monarchs were invited to pay tribute. The King looked deep in thought after adding his light.
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© GettyDanish royals
King Frederik and Queen Mary were seen quietly speaking with Charles ahead of placing their tributes.
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© GettyPrincess Catharina-Amalia
Future Dutch queen Princess Catharina-Amalia joined her parents, Queen Maxima and King Willem-Alexander, at the event in Poland.
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© GettyIn memory
King Felipe and Queen Letizia appeared visibly moved when it was their turn to place their candles.
