Pope Francis says sex outside marriage is 'not the most serious' sin
'Sins of the flesh are not the most serious,' the 84-year-old pontiff said during a press conference aboard the papal plane on Monday.
Pride and hatred are 'the most serious,' His Holiness added.
Francis made the comment in answer to a question about the Archbishop of Paris Michel Aupetit who resigned last week over an 'ambiguous' relationship with a woman.
Although Aupetit, 70, denied the relationship was sexual - Catholic priests take vows of celibacy - he resigned to prevent rumours from damaging the Church.
A diocese spokeswoman said at the time that 'he had an ambiguous behaviour with a person he was very close to', adding that it was 'not a loving relationship', nor sexual.
'When the gossip grows, grows, grows and takes away the reputation of a person, that man will not be able to govern... and that is an injustice,' Francis said.
'This is why I accepted Aupetit's resignation, not on the altar of truth, but on the altar of hypocrisy,' the pope said on the plane back from a trip to Greece.
'I ask myself, what did Aupetit do that was so serious he had to resign? If we don't know the accusation, we cannot condemn,' the pope added, urging journalists to investigate.
He said Aupetit had been condemned by 'public opinion, rumours. But what did he do? We know nothing'.