But Benedict turns out to be bad at hiding. He has repeatedly chimed in throughout Francis’ pontificate.

Their relationship — often depicted as a rivalry — has become an object of widespread fascination, most recently in the movie “The Two Popes,” where the two men are shown watching the 2014 World Cup final, rooting for competing teams. But the truth, as often is the case in the small Vatican city-state consumed with power politics and ideological rifts, shadowy maneuvering and gossip, is much stranger.

In April, only months after a groundbreaking Vatican conference called by Francis to address the Roman Catholic Church’s clerical sex abuse crisis, he released a 6,000-word letter holding forth on his views on the scandal’s origins. He put the blame on the swinging ’60s and sexual liberty, effectively undercutting Francis’ view that clericalism, or the abuse of power by priests, had allowed the scandal to fester.

That letter marked, for many critics, an egregious example of why having two popes — whose addresses are close but whose visions of the church are vastly apart — can be so confusing to the faithful.

But the book project appeared to mark an escalation.

“I believe that celibacy has great significance as an abandonment of an earthly realm,” Benedict wrote in the book, according to the excerpt in the French newspaper Le Figaro, adding that for priests staying on the path to God, “celibacy becomes really essential.”

On Tuesday, Archbishop Gänswein told the Austrian Catholic news agency Kathpress that at the request of the pope emeritus, Cardinal Sarah had called his publisher to ask that Benedict’s name and photograph be removed from the book’s cover, introduction and conclusion.

Benedict had not co-authored the book, Archbishop Gänswein explained, but had merely contributed “a short text of his on the priesthood.” He added that the pope emeritus had not signed a contract with the French publisher, Fayard.