It was the most unlikely friendship – a beautiful, wealthy American student in Washington DC and an elderly Irish priest living in semi-retirement, more than 3,000 miles away in Ireland. The correspondence between Jackie Kennedy and Fr Joseph Leonard began when she was 21 and he was 73.

“God will have some explaining to do to me if I ever see him,” the devastated first lady wrote to the priest in 1964 after her president husband was gunned down. “I have to think there is a God — or I have no hope of finding Jack again.”