Former Pope Benedict made a surprise entrance into St. Peter's Basilica to attend a ceremony at which his successor, Pope Francis, was elevating 19 prelates to the high rank of cardinal.
Benedict, who resigned a year ago, sat quietly wearing a long white overcoat in the front row along with other cardinals.
It was the first time he has attended a papal ceremony since his resignation, although he and Francis have met several times.
Pope Benedict XVI defrocked nearly 400 priests over just two years for molesting children according to a document obtained by the Associated Press.
The statistic, which relates to 2011 and 2012, emerged in the testimony of the Vatican's UN ambassador in Geneva, Archbishop Silvano Tomasi, before a UN committee.
The Holy See has had to defend itself before the UN human rights committee this week following reports of widespread child abuse in the Catholic Church.
Previously, the Vatican has only revealed the number of alleged cases of sexual abuse it had received.
Benedict welcomed his successor into his retirement residence, where the pair spoke inside a sitting room and joined each other in prayer.
Seven months after leaving the papacy, emeritus Pope Benedict XVI broke his self-imposed silence as he denied covering up for sexually abusive priests and defended Christianity to non-believers.
Pope Benedict released a letter to one of Italy's best-known atheists in the first work published by Benedict since he retired and his first-ever denial of personal responsibility for the sex scandal.
What made the letter published in La Repubblica even more remarkable was that it appeared just two weeks after the new pontiff, Pope Francis penned a similar letter to the newspaper's atheist editor.
The Vatican spokesman, the Rev. Federico Lombardi, said the appearance of the letters was pure coincidence.
Pope Emeritus Benedict XVI has been greeted by Pope Francis on his return to the Vatican, two months after he stepped down because of old age.
Benedict, who left the Vatican immediately after his resignation, will move into the Mater Ecclesiae monastery building within the City.
A Vatican spokesman has denied reports that Pope Emeritus Benedict XVI "is in poor health".
Concerns for the 86-year-old’s wellbeing were raised today after officials decided not to provide any television coverage of his return to the Vatican.
The Rev. Federico Lombardi said: "He is a man who is not young. He is old and his strength is slowly ebbing. However, there is no special illness. He is an old man who is healthy."
Pope Emeritus Benedict XVI, who resigned because of old age, will move into the Mater Ecclesiae monastery building within the Vatican.
Benedict chose to leave the Vatican immediately after his resignation to physically remove himself from the process of electing his successor.
His absence also gave workers time to finish up renovations on the monastery tucked behind St. Peter's Basilica that until last year housed groups of cloistered nuns.
In the compact, four-story building, Benedict will live with his personal secretary, Monsignor Georg Gaenswein, and the four consecrated women who look after him.
The building also has a small library, a study and a guest room for when his brother, Monsignor Georg Ratzinger, comes to visit.
Benedict XVI came home to the Vatican today for the first time since he resigned, beginning an unprecedented era of having a retired pontiff living alongside a reigning one.
The Vatican said Benedict, 86, was pleased to be back and that he would "dedicate himself to the service of the church with prayer."
Francis, the statement said, welcomed him with "brotherly cordiality."
Unlike the live, door-to-door Vatican-provided television coverage that accompanied Benedict's emotional farewell in February, the Vatican provided no television images of his return.
Benedict XVI has moved back to the Vatican, opening an unprecedented era in Catholic Church history where an "emeritus pope" and a ruling pontiff will live as neighbours.