The Duke and Duchess of Cambridge have described their visit to a Nazi concentration camp as "shattering", saying the site is a "terrible reminder of the cost of war".
William and Kate heard first hand about the horrors of Stutthof camp, now run as a museum, from survivors and also made a private tour of the site's crematorium, where the bodies of thousands of prisoners were burned.
The couple saw other evidence of the Nazi's attempts to exterminate the Jews, from a display of hundreds of pairs of shoes from Holocaust victims to the tiny wooden huts where prisoners slept three to a bunk.
William and Kate appeared in sombre and reflective mood as they toured the site, but the Duchess was not moved to tears.
The couple left a message in the visitors' book which they both signed: "We were intensely moved by our visit to Stutthof, which has been the scene of so much terrible pain, suffering and death.
"This shattering visit has reminded us of the horrendous murder of six million Jews, drawn from across the whole of Europe, who died in the abominable Holocaust.
"It is, too, a terrible reminder of the cost of war. And the fact that Poland alone lost millions of its people, who were the victims of a most brutal occupation.
"All of us have an overwhelming responsibility to make sure that we learn the lessons and that the horror of what happened is never forgotten and never repeated."
Later the couple visited the Polish port city of Gdansk, where large crowds turned out to see them.
British survivors of the concentration camp, Manfred Goldberg and Zigi Shipper, both 87, from London, made a special trip to the Stutthof camp - the first time they had returned to the site - to meet William and Kate and recount their experiences.
Mr Goldberg, who spent two phases of the war at the camp, said: "When I was here they found that the gas chamber was too small for their purposes - they couldn't gas people fast enough. They brought in two goods wagons on a railway line running at the back of the camp.
"They got engineers to make them air-tight and they used those as auxiliary gas chambers so they could kill people faster. Then they had the second problem because the crematorium couldn't burn the bodies fast enough, so periodically bodies were being piled up.
"A row of bodies, a row of timber, a row of bodies, a row of timber, until it was a sizeable pile and they would set fire to it and try to dispose of the bodies, in addition to the crematorium working 24 hours a day - those are some of memories from here."
He added: "I was feeling extremely nervous, I agonised before I agreed to come here, because I felt I'd put it all behind me. Nervous at facing the trials and tribulations.
"In 1946 when I was a youngster I was admitted to England, I didn't dream I would ever have the privilege of shaking the hand of a future King of this country."
William and Kate paid their respects during the visit by placing stones by the camp's Jewish memorial, accompanied by Mr Shipper and Mr Goldberg, who recited the El Male Rachamim, the Jewish memorial prayer for those who have died.
The elderly Holocaust survivors, who dedicate their lives to sharing their stories with the next generation through the Holocaust Educational Trust, met as young men in one of the sub-camps of Stutthof before being liberated in 1945.
Mr Shipper who survived four years in Lodz ghetto as well as deportation to Auschwitz-Birkenau, before being transported to Stutthof, said he "most probably" would not have returned to Stutthof if it was not for the royal visit.
He said: "I asked myself many times 'why don't I want to go to Stutthof?' I don't know. But when I came I realised how important it was."
The pensioner added that when he was a prisoner in the camp he was doing "nothing, no work at all".
He added: "We were just trying to keep warm, huddled together. Then after a while the inside people would go out so the outside people could get warm."
During the visit the duke appeared visibly moved as he left the crematorium - which features a large photograph of emaciated bodies - and was overheard apologising to the museum director for asking "so many questions."
They then met three polish survivors Maria Kowalska, 91, Mareka Dunin, 92, and Edward Anderson, 91.
After hearing details of their harrowing experiences at the hands of the Nazis, speaking through a translator, William asked: "You must wonder how people could commit such evil against another human?"
Mr Anderson said: "After we witnessed these things and lived through them, all we have left as a weapon is the knowledge to warn other people. To stop it happening again."
Later William and Kate met Lech Walesa, Poland's former president and leader of its peaceful pro-democracy struggle Solidarity, at the European Solidarity Centre - a museum and library in Gdansk devoted to the history of the movement.
Mr Walesa won the 1983 Nobel Peace Prize for leading Solidarity, six years later, Solidarity ousted the communists from power in peaceful negotiations.
Mr Walesa was democratic Poland's first popularly chosen president, from 1990 to 1995, but his authoritarian streak cost him a lot of popularity.
After having a brief tour of the museum which featured images of Mr Walesa, the Solidarity movement and the Gdansk shipyard which gave birth to the struggle, they met the white-haired statesman who chatted to the pair through an interpreter.
Outside the building Kate laid a single white rose and William a red rose at the base of the towering Monument to the fallen Shipyard Workers of 1970.