VATICAN CITY — Retired pope Benedict XVI never agreed to appear as the co-author of a controversial book on priestly celibacy, his personal secretary, Archbishop Georg Gaenswein, said Tuesday.

It was a remarkable disavowal of a work seen by many as both an attack on Pope Francis’ authority and a serious breach of Benedict’s promise to remain “hidden to the world” following his retirement in 2013.

In the book, Benedict is presented as arguing against a relaxation of the celibacy rule for priests, wading into a topic on which Francis is due to make a decision within a few weeks.

Gaenswein told the ANSA news agency that Benedict knew that Cardinal Robert Sarah was writing a book on the subject and sent him an essay on priesthood “authorizing him to do what he wanted with it.”

“But he never authorized any project for a co-authored book nor had he seen or authorized the cover,” Gaenswein added, calling the incident a “misunderstanding” in which Sarah acted “in good faith.”

Benedict has asked to have his name removed as co-author, Gaenswein said. Sarah tweeted that the work would now be presented as written by him “with the contribution of Benedict XVI.”