When Pope Benedict XVI suddenly announced exactly one year ago that he was resigning for health reasons, he sent shock waves around the world.
A second surprise was that after spending a short period of rest at the papal summer villa at Castelgandolfo, near Rome, he decided to take up residence again inside the walls of Vatican City where a former convent had been converted for his personal use.
How would the ex-pontiff and the new reigning Pope manage to co-habit?
When rival popes were elected for political reasons in different parts of Europe during the late Middle Ages, it caused confusion and conflict within the church.
But in this case there has been an exceptionally smooth transition from one papacy to the next.
Pope Benedict, or rather Emeritus Pope Benedict to give him his new official title, lives only a few hundred metres away from his successor Pope Francis.
The two popes visit each other occasionally and communicate fairly frequently by telephone and letter.
Pope Benedict, who for the previous eight years was one of the world's highest profile public figures, now keeps deliberately out of the limelight.
"He lives discreetly without a public life, but that doesn't mean he is isolated," says Father Federico Lombardi, the Vatican's official spokesman.
He also plays Mozart and Beethoven on the baby grand piano that he brought with him when he left the spacious papal apartments in the Apostolic Palace.
The same four consecrated laywomen - who kept house for him when he was pope - continue to run his more modest new household.
They have been photographed with him, taking his daily walk with the aid of a black cane in the well manicured Vatican gardens behind St Peter's Basilica, an oasis of tranquillity, situated in the heart of Rome, yet sheltered from the din and traffic chaos of the Italian capital.
Business as usual
Benedict was guest of honour at a luncheon party given by Pope Francis at the Casa Santa Marta - the Vatican guest house where he has chosen to live - to celebrate his own 77th birthday just before Christmas.
Writing a few days later to the dissident Swiss theologian Hans Kueng - with whom he had had a serious falling out years ago, banning him from teaching at a Catholic university - the former Cardinal Ratzinger showed a much more conciliatory attitude than he had shown during his years in positions of power inside the Vatican.
"I am grateful to be bound by a great identity of views and by a deep friendship with Pope Francis," he wrote to Prof Kueng. "My only final task is to support his papacy in my prayers."
Superficially, nothing much has changed inside the Vatican during the year of two popes.
Some key new appointments - such as that of the pope's deputy, or secretary of state, have been made by Pope Francis - but the weekly rhythm of business inside the world's smallest sovereign state continues as before.
Bishops from around the world are beginning to arrive again in national groups to make their annual five-yearly report to Rome on what is going on in their dioceses.
Heads of state and government are received in private audience by Pope Francis.
Attendance at the Pope's Wednesday General Audience and his regular Sunday blessing of the faithful in St Peter's Square has more than doubled since Pope Benedict's resignation.
This reflects the growing international popularity of his successor, the first Pope from the Americas, who has not surprisingly been declared person of the year by Time Magazine and been celebrated by cover stories in the New Yorker and even the pop music magazine Rolling Stone.
Archbishop Georg Gaenswein has been Pope Benedict's private secretary for nearly a decade and continues to live in the convent with the former pontiff.
He is one of the few people who see both popes on a daily basis, as he is also responsible for arranging the diary and engagements of Pope Francis as Head of the Papal Household.
"I try to be a bridge between both popes, and so far it has worked very well. I hope the two bosses are happy," the archbishop told Reuters news agency.