The King has praised former Pope Benedict XVI’s “constant efforts to promote peace and goodwill to all people” after his death aged 95.
Charles expressed his “deep sadness” at Benedict’s death in a message to his successor Pope Francis, as the head of the Roman Catholic Church in England and Wales, Cardinal Vincent Nichols, and the Archbishop of Canterbury, Justin Welby, also paid tribute.
Benedict became the second pontiff in history to visit the UK in 2010 when he met the Queen and made a historic address at Westminster Hall.
He was the first pope in 600 years to resign and was replaced by Francis in 2013.
Francis will celebrate Benedict’s funeral Mass in St Peter’s Square in Vatican City on Thursday, the Vatican said.
In a statement, Charles paid tribute to Benedict and recalled visiting him at the Vatican in 2009.
He said: “Your Holiness, I received the news of the death of your predecessor, Pope Emeritus Benedict XVI, with deep sadness.
“I remember with fondness my meeting with His Holiness during my visit to the Vatican in 2009. His visit to the United Kingdom in 2010 was important in strengthening the relations between the Holy See and the United Kingdom.
“I also recall his constant efforts to promote peace and goodwill to all people, and to strengthen the relationship between the global Anglican Communion and the Roman Catholic Church.”
Mr Nichols told PA the news agency: “I think the news this morning came still with an element of surprise, even though we were warned a few days ago that his health had deteriorated very significantly.
“I was consoled by a comment I heard that somebody had made in Rome a couple of days ago, where they put it rather beautifully – they said, ‘The angels are gathering, they’re coming to take him home’.”
The Cardinal also praised Benedict’s “landmark” trip in 2010 when he became the second pope in history to visit the UK, reminiscing about the German theologian meeting the Queen in Edinburgh and an address he made at Westminster Hall, for which “every living prime minister was present”.
He added: “I remember when the visit was being arranged, the whole expectation was the Pope would come to London but he said, ‘No, first of all I want to see the Queen’.
“And the Queen was in Balmoral, but she came to Edinburgh and he arrived in the United Kingdom in Edinburgh in order to make sure that his first visit and his first steps in the United Kingdom were with the Queen.
“Now, it’s worth remembering they’re the same age, the Queen died at 95, Pope Benedict has died at 95. And there was a great esteem between them, a deep respect.
“I was not far away from that first visit and there was not only respect but there was also a little bit of humour as well that the car that had been provided for the Pope to travel from Edinburgh Airport to Holyrood House Palace she thought was a bit small and it had darkened windows, and she said, ‘That won’t do, it’s got to be something which people can see you (in).
“The Queen and the Pope understood what it was to be in service more or less for a lifetime.”
Joseph Ratzinger was elected as the 265th pope on April 19 2005, aged 78, and chose the name Benedict.
He served until February 2013 before becoming the first pope in 600 years to resign, citing his old age and declining health.
Mr Welby hailed Benedict as “one of the greatest theologians of his age”.
In a statement, he said Benedict was “committed to the faith of the Church and stalwart in its defence”.
Prime Minister Rishi Sunak wrote on Twitter: “I am saddened to learn of the death of Pope Emeritus Benedict XVI.
“He was a great theologian whose UK visit in 2010 was an historic moment for both Catholics and non-Catholics throughout our country.”
Labour leader Sir Keir Starmer said: “His state visit in 2010 was a historic and joyous moment for Catholics in Britain.”