Piero Piperno was one of more than 4,200 Jews who in October 1943 were given sanctuary in the religious houses of the city on the secret orders of the Venerable Pope Pius XII.
There, Mother Riccarda Beauchamp Hambrough, who had moved from London to Rome to join a newly revived order of Bridgettine nuns, fed and consoled him and his family and also dissuaded German soldiers from searching her convent for them.
In a new book called Courage and Conviction, Mr Piperno tells Joanna Bogle, a Catholic author and journalist, about his memories of the English nun whose Cause was last year taken up by the Vatican.
He explained how he and his family fled from Sienna to Rome as the Nazis began to round up Italian Jews for deportation to the concentration camps.
As a 15-year-old in a group of 13 Jews hidden in the Casa di Santa Brigida, the Bridgettine mother house in Rome, he remembers how Mother Riccarda would bring them food and console them.
“What I remember most about Mother Riccarda was her smile,” he said. “She was so sweet and kind always, and her smile was beautiful, radiant. She helped always – you instinctively went to her when you were troubled, and she would soothe things.
“She was also very pretty – you can’t tell that from her photograph, but in real life she was really beautiful.
“She was English, very much so, but she had fluent Italian. She put everyone at ease. We called her Mamima – ‘little mother’.” He said that she could sometimes be overshadowed by Blessed Elisabeth Hasselblad, the abbess, “who was definitely the lady in charge and who had a big personality”.
But he added: “Our Mamima, Mother Riccarda, was different – she was quiet, she did things in a quiet, pleasant way. We all loved her very much.” He said when they arrived at the convent in Rome’s historic Piazza Farnese his mother was too scared to tell the abbess that they were Jewish.
Attempting to disguise themselves, they attended Mass on Christmas Day but the mother eventually decided to admit their identity.
They were then told by the nuns to “live our own beliefs, that we must not feel any need to pretend, and that we must live and pray as Jews”.
The nuns “gave us back our dignity”, Mr Piperno said, adding: “It is impossible to explain what that meant to us. We felt human again.”
One nun, the Rev Mother Thekla, said that Mother Riccarda “above all had a profound respect for these Jewish guests.
“Mother Riccarda was an extremely discreet woman – she knew when to talk and when not to talk, she was gentle and calm, and she was highly educated,” she said.
“She spoke good German, so she was able to speak with confidence to German soldiers if they came around.”
The nuns also hid Vello Salo, an Estonian deserter from the German Army, who after the war was ordained as a Catholic priest.
Mrs Bogle’s book has been published by Gracewing just 18 months after a file on Mother Riccarda was sent to the Vatican’s Congregation of Causes for Sainthood to be studied by historians and theologians.
The nun’s Cause was opened in July 2010 along with that of Sr Katherine Flanagan.
Both nuns belonged to an Order called the Most Holy Saviour of St Bridget, nicknamed “the hot cross bun nuns” because of the crosses covering the tops of their wimples.