Ex-pope's shadow Vatican role in the spotlight

Ex-pope Benedict XVI seems to have broken his silence recently over key Catholic issues and his comments have raised serious questions within the Church about the extent to which there are, in fact, two "men in white" at the Vatican.

In 2013, Benedict became the first pontiff to resign in almost 600 years. He chose to be known thereafter as "pope emeritus" and said he would live "hidden from the world" in a former convent inside the Vatican grounds.

While he initially stuck to his promise to carry out a life of quiet contemplation and academic research, he has since weighed in on the explosive issues of clerical sex abuse and whether the priesthood could be opened to married men.

This week, Benedict's contribution to a book on celibacy was seen as a strategic attempt to undermine his successor Pope Francis and boost the cause of a combative ultra-conservative wing of the Church.

Experts say the problem is that no rules were drawn up to define what role Benedict should play after he stepped down as head of the church.

"There were hints of a problem right from the start", when Benedict gave up the papal hat but not the postal address, Richard Gaillardetz, Catholic theology professor at Boston College, told the National Catholic Reporter.

"The publication of views on controverted issues, when offered by a man who insists that he too still deserves the title 'pope' (albeit pope emeritus), who continues to wear papal garb and who still resides in the Vatican, is deeply problematic," Gaillardetz said.

Even Benedict's supporters said he should have used his given name, Joseph Ratzinger, when signing his contribution to the book.

Historian Francesco Margiotta Broglio, head of Italy's religious freedom commission, told La Stampa, "Ratzinger should neither write nor speak. If he continues to go against the reigning pope, he could become an anti-pope."