The story of Pope John Paul II's close relationship with a married woman have been revealed after hundreds of letters and photographs were shown to the BBC.

The documents between the former Pope, who died in 2005, and the Polish-born American philosopher Anna-Teresa Tymieniecka have been hidden from public view for years in the National Library of Poland.

A BBC Panorama programme aired tonight will explore whether the pontiff fell in love with Tymieniecka. However there is no evidence in the documentary that Pope John Paul broke his vow of celibacy.

The Vatican has distanced itself from the upcoming programme and described the content as being "more smoke than fire". John Paul II was fast-tracked to sainthood in 2011 and canonised by Pope Francis in 2014.

The correspondence between the two reveals "a rarely seen side of the pontiff", according to the BBC. The friendship began in 1973 when Tymieniecka contacted the future Pope, Cardinal Karol Wojtyla, when he was Archbishop of Krakow.

Initially the cardinal's letters were formal but increasingly became more intimate as their relationship developed. The two decided to work together on expanding the cardinal's book 'The Acting Person'.

By 1974 the Pope wrote he was re-reading Tymieniecka's letters several times because they were "so meaningful and deeply personal". The pair met frequently, either with his secretary or alone, and went on country walks and skiing holidays together. She even joined him on a group camping trip and pictures show her visiting the Vatican at least once.

Although the BBC has not seen any of Tymieniecka's letters, it appears she revealed intense feelings for him because "his letters immediately afterwards suggest a man struggling to make sense of their friendship in Christian terms".

Cardinal Wojtyla became Pope John Paul II in 1978 but wrote to Tymieniecka shortly afterwards to insist their regular correspondence continues.

"I am writing after the event, so that the correspondence between us should continue. I promise I will remember everything at this new stage of my journey."

John Paul II was fast-tracked to sainthood over a period of just nine years, considerably quicker than the arduous process normally takes. Usually the Vatican asks to see all public and private writings when a candidate is being considered for sainthood. It is not known whether these letters were seen before John Paul was canonised.

The programme will be aired at 20.30 on BBC One tonight.