Hundreds of letters and photographs that tell the story of Pope John Paul II’s close relationship with a married woman, which lasted more than 30 years, have been shown to the BBC.
The letters to Polish-born American philosopher Anna-Teresa Tymieniecka had been kept away from public view in the National Library of Poland for years.
The documents reveal a rarely seen side of the pontiff, who died in 2005.
There is no suggestion the Pope broke his vow of celibacy.
The friendship began in 1973 when Ms Tymieniecka contacted the future Pope, Cardinal Karol Wojtyla, then Archbishop of Krakow, about a book on philosophy that he had written.
The then 50-year-old travelled from the US to Poland to discuss the work.
Shortly afterwards, the pair began to correspond. At first the cardinal’s letters were formal, but as their friendship grew, they become more intimate.
The pair decided to work on an expanded version of the cardinal’s book, The Acting Person. They met many times – sometimes with his secretary present, sometimes alone – and corresponded frequently.