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.

In 1974, he wrote that he was re-reading four of Ms Tymienkiecka’s letters written in one month because they were “so meaningful and deeply personal”.

Photographs which have never been seen before by the public reveal Karol Wojtyla at his most relaxed. He invited Ms Tymienkiecka to join him on country walks and skiing holidays – she even joined him on a group camping trip. The pictures also show her visiting him at the Vatican.

“Here is one of the handful of transcendentally great figures in public life in the 20th Century, the head of the Catholic Church, in an intense relationship with an attractive woman,” says Eamon Duffy, Professor of the History of Christianity at Cambridge University.