The official newspaper of the Holy See released this photo of Pope Francis greeting his predecessor, Benedict XVI, in the hill town of Castel Gandolfo, south of Rome, before Francis had lunch with his “brother” in a historic — and potentially problematic — melding of the papacies that has never before confronted the Catholic Church.

VATICAN CITY — Sharing lunch is rarely historic, except perhaps when the two people dining are a living pope and his predecessor.

On Saturday, the pope emeritus, Benedict XVI — who broke church tradition by resigning rather than dying in office — ate with Pope Francis at Castel Gandolfo, the hilltop villa where Benedict is living, while reporters waited outside for any scraps of news about how the meeting went.

Vatican officials gave no word about what the past and present leaders of the Roman Catholic Church discussed, and even rebuffed questions about what they ate. They did, however, paint a picture of a seamless transition: when Benedict offered his successor the “place of honor” during shared prayers, the Vatican said, Francis demurred, suggesting that they kneel side by side as “brothers.”

But the reality of a pope and an emeritus pope will probably be more complicated, a fact driven home recently with the publication in one of Italy’s racier gossip magazines of paparazzi-style photos of the 85-year-old Benedict strolling with his personal secretary through the private gardens of his temporary home at Castel Gandolfo. The photographs were a vivid reminder of the uncharted territory the Vatican has entered, and the potential trouble it could bring.

During this transition, the new pope, the cardinals and the Vatican have gone out of their way to express affection and gratitude toward the pope emeritus. But each time they do, it does more to deepen the complexity of the relationship than to clarify it. The Vatican has rejected any prospect of meddling by Benedict. But concern remains among some cardinals, Vatican officials and church experts.

“There is a duality, and even if the old pope says he will retire from the world, he will be an awkward presence,” said Roberto Rusconi, a church historian at Third University of Rome. But he dismissed the possibility of a new schism like the one that occurred with the death of Pope Gregory XI in 1378. Afterward, one pope lived in Avignon, France, and another in Rome. Such divides were fomented by secular rulers, he said, with the dueling popes each claiming legitimacy.

Even so, he said, better to keep Benedict inside the Vatican — in its own way a prison of sorts, like any cloistered convent — because “not everyone might resist from asking the old pope’s opinion.” Rusconi added, “That just can’t happen.”

The ‘pope emeritus’

Still, this has been an unexpected amount of attention lavished on Benedict, a man who had pledged to live out his days “hidden from the world.”

In a few weeks, Benedict will move into a nondescript convent not far from the sumptuous apostolic palace where he lived as the leader of the church. He is now known as “pope emeritus.”

Already, canonical experts have raised questions about the correctness of Benedict’s adopting that title. Writing in La Civilta Cattolica, a Jesuit magazine, the Rev. Gianfranco Ghirlanda, a former rector of the Pontifical Gregorian University, argued that a more appropriate title would be “bishop emeritus of Rome, like any other diocesan bishop who steps down.”

The Vatican has played down the novel accommodation. To have the pope emeritus “present, near, discreet” will provide a “great enrichment” for the new pope, the Vatican spokesman, the Rev. Federico Lombardi, told reporters recently.