A new BBC documentary claims that the pope, who died in 2005 and was canonized in 2014, corresponded with a now-deceased Polish philosopher at length.
In one letter, he writes that she is "a gift from God."
"If I did not have this conviction, some moral certainty of Grace, and of acting in obedience to it, I would not dare act like this," he wrote, according to the BBC.
Tymieniecka, who has since died, sold the collection of more than 250 letters to the library in 2008.
According to Agence France Presse, the Vatican said there is "nothing out of the ordinary in the fact that pope John Paul II had close friendships with different people, whether men or women."
"Nobody will be amazed at this information," a spokesman the Vatican said, according to the AFP.
Tymieniecka collaborated with the former pope on a book about philosophy that he had started writing while he was a Cardinal in Poland.