The BBC has received hundreds of letters and pictures depicting the close relationship between Pope John Paul II and Anna-Teresa Tymieniecka, a married woman originally from Poland.
The friendship lasted for over 30 years, though the letters do not offer any suggestion that the Pope, who died in 2005, violated his vow of celibacy.
The two first came into contact in 1973, when Tymieniecka asked then-Cardinal Karol Wojtyla to comment on a philosophy book he had written. Over time they became closer and even went on holidays together.