VATICAN CITY (AP) - Pope Emeritus Benedict XVI comes home on Thursday to a new house and a new pope, as an unprecedented era begins of a retired pontiff living side-by-side with a reigning one inside the Vatican gardens.

All eyes will be on Benedict's physical state as he is welcomed by Pope Francis at his new retirement home, a converted monastery tucked behind St Peter's Basilica. The last time he was seen by the public - on March 23 - Benedict appeared remarkably more frail and thin than when he left the Vatican on his final day as pope three weeks earlier.

The Vatican spokesman, the Reverend Federico Lombardi, has acknowledged Benedict's post-retirement decline but insists the 86-year-old German is not suffering from any ailment and is just old.

"He is a man who is not young: He is old and his strength is slowly ebbing," Rev Lombardi said this week. "However, there is no special illness. He is an old man who is healthy."

Since his Feb. 28 resignation, Benedict has been "hidden to the world" as he himself predicted, living at the papal residence in Castel Gandolfo, in the hills south of Rome. He chose to leave the Vatican immediately after his resignation to physically remove himself from the process of electing his successor and from Pope Francis' first weeks as pontiff.

His absence also gave workers time to finish up renovations on the monastery on the edge of the Vatican gardens that until last year housed groups of cloistered nuns who were invited for a few years at a time to live inside the Vatican to pray for the pontiff and church at large.

In the small building, with a chapel attached, Benedict will live with his personal secretary, Monsignor Georg Gaenswein, and the four consecrated women who look after him, preparing his meals and tending to the household. Inside the small building, Benedict has at his disposal a small library and a study. A guest room is available for when his brother, Monsignor Georg Ratzinger, comes to visit.

"It is certainly small but well-equipped," Rev Lombardi said.

When Benedict announced his intention to resign - the first pontiff to do so in 600 years - questions immediately swirled about the implications of having two popes living alongside one another inside the Vatican.

Benedict fuelled those concerns when he chose to be called "emeritus pope" and "Your Holiness" rather than "emeritus bishop of Rome". He also raised eyebrows when he chose to continue wearing the white cassock of the papacy.

Given the political intrigues that plague the Vatican, it was not much of a stretch of the imagination to wonder if some cardinals, bishops and monsignors - not to mention ordinary Catholics - might continue making Benedict their point of reference rather than the new Pope.

However, Benedict made clear on his final day as pope that he was renouncing the job and pledged his "unconditional reverence and obedience" to his then-unknown successor. It was a pledge he repeated in person on March 23 when Pope Francis went to have lunch with him at Castel Gandolfo.

It was during that visit that the world saw how frail Benedict had become in the three weeks since his emotional departure from the Apostolic Palace: Always a man with a purposeful walk, he shuffled tentatively that day, using his cane.

Pope Francis, for his part, seems utterly unfazed by the novel situation unfolding. He has frequently invoked Benedict's name and work and has called him on a half-dozen occasions, making clear he has no intention of ignoring the fact that there's another pope still very much alive and now living on the other side of the garden from the Vatican hotel where he lives.

Pope Francis' gestures to Benedict during that March 23 visit were also remarkable: He refused to pray on the special papal kneeler in the small chapel of Castel Gandolfo, preferring to join Benedict on a kneeler in the pews, and referring to his predecessor as his "brother". Now that they're neighbours, they might bump into one another on walks in the Vatican gardens or at the shrine to the Madonna on the top of the hill, just a stone's throw from Benedict's new home.