The former the archbishop of Canterbury, Rowan Williams, told Vatican Radio that the Pope's historic announcement on Monday that he was to retire was "not a total surprise".
Pope Benedict XVI made the announcement in Latin at the end of a meeting of cardinals where he had been discussing three forthcoming canonisations.
Dr Williams, who left Canterbury at the end of 2012 to become Master of Magdalene College, Cambridge, told Vatican Radio, that in a private meeting in the Vatican last March, the two Church leaders discussed the pressures of office and how much each of them wished to be able to do "a bit more thinking and praying".
The former leader of the worldwide Anglican Communion, who has written to the Pope privately following the news, was aware that Pope Benedict was increasingly recognising his own frailty.
Dr Williams said the resignation could aid ecumenical relations because it has helped to "demystify the papacy - the pope is not like a sort of God-King who goes on to the very end". He said it depicted a bishop of Rome "who convenes, mediates between, manages the fellowship of the bishops" - a role "slightly more functional, slightly less theologically top heavy".
"We look for some more profound and reflective theology from him, of the kind that's made his encyclicals so wonderfully fruitful as a resource for the whole Christian family," he said.
The Pope's elder brother, Fr Georg Ratzinger, 89, said yesterday his 85-year-old brother had been thinking about resigning for months because the question of his age was weighing on him.
"When he got to the second half of his 80s he felt that his age was showing and that we was gradually losing the abilities he may have had, and that it takes, to fulfil this office properly."
He added: "It's simply the case that people didn't used to become as old as they do today. He reached an age that only very few of his predecessors had reached."
Fr Ratzinger, who lives in Bavaria where the brothers grew up, told the German news agency dpa that Benedict XVI was having increasing difficulty walking and that his resignation was part of a "natural process".
Today Archbishop Vincent Nichols, on behalf of the bishops of England and Wales, wrote to Pope Benedict, saying: "We recognise the courage and integrity of your decision to step down from the See of St Peter. We assure you of our support, while very conscious of our profound sense of loss."
The Vatican newspaper, L'Osservatore Romano, reported that the Pope took the decision almost a year ago, following a trip to Mexico and Cuba which exhausted him. The Archbishop of Rio, Orani Tempesta, recalled the Pope saying last year that either he - or a successor - would attend World Youth Day in Brazil in 2013, The Independent reported.
Fr Lombardi said today that the Pope would celebrate Ash Wednesday not in the Basilica of Santa Sabina but at St Peter's, as the Vatican anticipates greater numbers of clergy and faithful wanting to attend.
Fr Lombardi said today that the teaching document on faith that the Pope has been working on will not be published before he resigns as Pope. It had been seen as a natural conclusion to his papal encyclicals on charity and hope.
The Vatican said it hopes the Catholic Church will have a new Pope by Easter following yesterday's Pope Benedict XVI's shock announcement that he is to resign with effect from 28 February.
The Holy See spokesman, Fr Federico Lombardi, said that the Pope will first go to live at his summer residence Castel Gandolfo. Once his successor is elected Benedict XVI would live in a monastery that formerly belonged to an order of enclosed nuns at the Vatican.
In the highly unusual move, the 85-year-old Pope told a meeting of cardinals in the Vatican that he would leave office on 28 February for health reasons.
Italian journalist Giovanna Chirri, who broke the story for news agency ANSA because she was able to understand the Pope's statement in Latin, said that "my knees felt weak as I fought to keep my nerve" when she realised the Pope was announcing his resignation.
The Church now finds itself in uncharted waters. An official title for the "pope emeritus" has yet to be agreed upon and a date is not yet known for the start of the conclave at which cardinals will begin the process of electing a successor.
Fr Lombardi confirmed yesterday that Pope Benedict would play no part in the election of his successor. He stressed that following his retirement Benedict XVI would be surrendering the office of pope completely.
Fr Lombardi said Pope Benedict's decision to resign was not due to any specific illness. He said the Pope had decided to step down because he felt his powers waning because of his advanced age. Asked why Pope Benedict had announced his decision at a consistory to announce three canonisations, Fr Lombardi said it presented the first opportunity to address cardinals directly before Lent given that he had decided to retire on 28 February.
On the question of whether Pope Benedict would himself remain enclosed at the monastery on Vatican Hill where he will make his permanent home, Fr Lombardi said he would be free to live as he pleased and was expected to devote the remainder of his life to study, prayer and reflection.
Cardinal Angelo Sodano, Dean of the College of Cardinals, said today's announcement came as "a bolt out of the blue".
Archbishop Vincent Nichols, President of the Catholic Bishops' Conference of England and Wales, said the news had "shocked and surprised everyone" but praised him for "his courage and his decision".
Listen to the Pope's announcement in Latin (Vatican Radio)
Above: Pope Benedict when he was elected in 2005, and now. Photos: CNS