Monday marks the 75th anniversary of the liberation of Auschwitz and Ryan Tubridy spoke to Rainer Hoess, who, at Ryan's urging, began by letting listeners know, in no uncertain terms, his background:

"I'm the grandson of Rudolf Hoess, who was the former and founder of the Auschwitz extermination camp in 1940. So he was responsible for more than 1.3 million killings in that camp."

It's quite the opening statement. The extraordinary thing – one of the extraordinary things – about Rainer Hoess' story, is the fact that his parents never told him what his grandfather's monstrous legacy was. Rudolf Hoess – who was executed 18 years before Rainer was born – created the Auschwitz camp, becoming infamous as he carried out the Nazis' Final Solution, using Zyklon B gas to ruthlessly exterminate large amounts of prisoners at a time.

"He killed, in 56 days, more than 400,000 people by gas."

Rainer's father lived in Auschwitz with his parents and siblings. According to Rainer, the children of Nazi families living on the camp had signs around their necks with their names on them, so they wouldn't inadvertently get mixed up with prisoners' children. And though they had green fields and ponds and animals to entertain them, the horror was never very far away:

"What was really specific, like the saying of my grandmother, that she said to the kids with the greenhouses, 'So before you eat the vegetables, or the fruits, you have to wash it while it's full of ash'."

It took Rainer several steps to discover who his grandfather was. The first was in a boarding school, when he got into trouble and was, as he puts it, sentenced to work with the school gardener, who had been a prisoner at Auschwitz. His German teacher asked if he wanted to visit a concentration camp. The young Rainer Hoess didn't know what a concentration camp was, but his teacher had a motorbike, so he agreed to go with him. The teacher took him to Dachau and there he saw plaques proclaiming that Rudolf Hoess was responsible for a million deaths.

"And immediately I called my father and asked him how that guy belongs to us, if it's part of our family and he said, 'No, no, it's a spelling mistake. It should [be] called Rudolf Hess with an e.' "

The second step was the discovery of books in his parents' house when he was 15. The books were The Commandant of Auschwitz: Memoirs of Rudolf Hoess and People in Auschwitz by Hermann Langbein, a survivor of the camp. His father punished him for the discovery, but his mother allowed him to read them.

"I read both books. I was completely shocked [by] what happened to the family and that everybody is denying it. And then I left my home [at] the age of 15."

Ranier didn't react well to the discovery of his family's secret and fell into alcohol, drugs and violence. When he became a father himself at the age of 17, he says it led to him turning his life around.

The full remarkable story of how Rainer Hoess discovered his family's dark past and how he became what he calls a tolerance preacher, is here.

Niall Ó Sioradáin