ROME—Four years after he announced his resignation on Feb. 11, 2013, emeritus Pope Benedict XVI is “in perfect mental and spiritual” health, according to his former spokesman, who remains a close collaborator.

Father Federico Lombardi, currently president of the Vatican Foundation Joseph Ratzinger-Benedict XVI, told Vatican Radio that even though the pope emeritus remains perfectly lucid, “his physical strength is debilitating little by little.”

There are no particular illnesses, Lombardi said, but “it’s noticeable that fragility increases with age. Whatever the case, he’s on foot, walking around the house.”

Speaking to the Italian TV outlet Tg2000, Lombardi said that since he was close to Benedict in the months previous to his resignation, it was clear that he was feeling at the limits of his possibilities to carry out his role.

“Certainly, Benedict XVI made real what was simply a possibility. With [his resignation] he opened an eventual pathway for his successors to take it. This way, if they found themselves in a similar situation, freely before God, they could reach a similar conclusion,” Lombardi said.

Francis has praised his predecessor’s decision to resign on countless occasions. For instance, speaking to the Argentine Newspaper La Nación, he defined Benedict as a “revolutionary” for having made that choice.

Pope Francis said Benedict’s resignation “exposed all the problems of the Church,” and was itself “an act of government, his final act of government.”

Francis has also praised Benedict for having launched reforms that he’s trying to complete.

More often than not, for instance, whenever Francis is asked about the need to fight clerical sexual abuse, the Argentine praises his predecessor for being “the brave one who helped so many open this door.”

Benedict, Francis has said, was the man doing the “hidden works” that became the foundations for “taking the lid off the pot,” but also publicly acknowledged that it was necessary to “clean up the dirt of the Church.”

The pope emeritus will celebrate his 90th birthday on April 16, and even though he broke his self-imposed silence last year to mark his 65th anniversary of priestly ordination with a ceremony at the Vatican headed by Francis, at the moment no such events are planned.

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Due to age and a limited vision, Benedict no longer writes, but with the consent of his successor, last year three lengthy interviews were published.

One was a 2015 conversation with Jesuit Theologian Jacques Servais, on the doctrine of justification and faith. Then there was one he held with his Italian biographer, Elio Gueriero, published in the book Servant of God and Humanity: The Biography of Benedict XVI, prefaced by Francis.

Last but not least, there was the book-length interview, Final Conversations, with German journalist Peter Seewald, with whom the pontiff had already done two similar projects. Released in several languages, including English, this book represented the first time in history a pope described his own pontificate after it ended.

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As it was evident in his preface to Gueriero’s book, Francis and Benedict have a good rapport, and the two communicate semi-regularly, with the pope paying his predecessor a visit before each of his international trips and on some important dates. For instance, last November after the consistory of new cardinals, when all went to see Benedict at the Monastery Mater Ecclesia, within Vatican territories.