The king and I -- My take on the reign of Charles III: OPINION

With her impeccable sense of timing, the late queen saved the best until last with her tribute to her eldest son, the future King Charles III. Her Majesty spoke, from the heart -- as a mother. Her words about Charles were among the warmest public remarks she ever made about him in public.

As she addressed those in the packed room there to mark Charles's 70th birthday, she could not have been more proud of him.

"It is a privilege for any mother to be able to propose a toast to her son on his seventieth birthday. It means that you have lived long enough to see your child grow up. It is rather like – to use an analogy I am certain will find favour – planting a tree and being able to watch it grow," she said.

The late queen spoke too of Charles being a champion of conservation and the arts, a great charitable leader as well as a wonderful father. "Not a man who accepts praise easily, he was deeply touched by her words," a close source said.

Now that Her Majesty has passed, it is Charles's head that wears the the heavy crown. Just days into the role, he has already steadied the ship through his thoughtful speeches and his heartfelt television address. He has earned praise for his composure too -- although a leaky pen did cause him to understandably let his guard slip.

On Thursday, he was at Highgrove House, his residence south of Tetbury -- not "resting" as some media outlets put it, but speaking to world leaders and governor generals, who wished to express their condolences, Including King Salman bin Abdulaziz Al Saud, of Saudi Arabia, Rwandan President Paul Kagame, Dame Cindy Kiro, the governor general of New Zealand and the presidents of Italian and Germany.

Today he rejoins the Queen Consort on a visit to Wales, the final leg of "Operation Spring Tide," him taking the throne and visiting all the U.K. capitals and their people.

Many are now asking: What sort of king will Charles be? In a YouGov poll last week, 63% of Britons polled said he is holding up well and they backed him. But this is a king who cares what people think, but is unconcerned by opinion polls. Unlike politicians, he, like his mother before him, will serve until he dies.

I have had the honour of interviewing His Majesty on a couple of occasions, as well as travelling around the world on royal tours with him for more than 30 years, for the biography I wrote about him and once for the Evening Standard.

We talked on the record about a whole range of issues that mattered to him, and how they are all interconnected. During his visit to Japan for the enthronement of the new emperor, Naruhito, we discussed the financial implications of a sustainable economy and the circular and blue economy.

On both occasions, I came away deeply impressed that he is not only very well informed, a man of vision, a leader and great convener, but he is also a man of deep faith, who has the courage of his conviction.

We talked about London's scourge of knife crime and violence on our capital city's streets.

The prince was quick to point out that his "causes" are all linked and stressed he does not blindingly leap from one subject or concern to another, as some have suggested.

He reminded me that crime and the built environment are intrinsically connected, and lamented the fact that developers and council planners had failed to grasp it, either deliberately or through ignorance.

He believes London is a unique "city of villages" now under assault from "faceless" towers, and is "poorly conceived" – so-called mega-developments.

He said of architecture as far back as 1987, "In the space of a mere fifteen years in the sixties and seventies...the planners, architects and developers of the City wrecked the London skyline and desecrated the dome of St Paul's." His opinion hasn't changed.

Prince Charles's thoughts on architecture and the built environment have long been contentious, but have merit and widespread support among the general public. He believes developers, architects and town and city planners must go back to the drawing board.

He believes retaining London's squares was important, he said, because in this way people get to know their neighbors and ultimately develop a sense of community and of responsibility for that community and the people within it.

As a result, people living there would, ultimately, as they had in the past, largely "police themselves." He told me he had spoken at length with the U.K. capital city's elected Labour mayor, Sadiq Khan, about it, but, "I can't seem to get through to him," said the then Prince of Wales.

My conversation with the prince, aboard a flight, was not exclusively serious. There was humour, too – with Charles that is almost inevitable. He is a very funny man, with a quirky sense of humour formed from his love of Spike Milligan and The Goons.

But he, like the queen is a man of deep faith. It is what is helping him through the pain of losing his father and now his mother in quick succession. He retreated to his sanctuary in Highgrove, for a period of prayer and reflection away from the public gaze.

Successive English (and later British) monarchs since Henry VIII have all been known by the title Defender of the Faith – Fidei Defensor (feminine: Fidei Defensatrix). It was bestowed on the tyrannical Henry by Pope Leo X on Oct. 11, 1521, because he was a good Roman Catholic.

When Henry broke with Rome nine years later in 1530 and was established as head of his new Church of England, the title was revoked by the then-Pope.

Bur in 1544, the English Parliament conferred the same title, "Defender of the Faith", on the king and all his successors, for being Supreme Governor of the Church of England.

It meant too that the monarch was formally of higher rank than the sitting Archbishop of Canterbury.

In 1952, when Queen Elizabeth II ascended the throne on the death of her father, she too, became Defender of the Faith and her coronation confirmed that. It was a very different, more religious and faithful society back then – an Anglican-led Christian society. Many of her subjects still believed that the queen had actually been appointed by God.

Charles III has become head of a very different, multi-denominational nation, and where, by the time his son, William, succeeds him, according to census analysis, Christianity could already no longer be the prevailing faith.

Studies predict all Christians, including both Protestant and Roman Catholic, will be in the minority in the U.K. by the middle of this century.

The king has long faced criticism over his acceptance of other faiths and willingness to embrace and understand other views and beliefs. It is something for which he should be praised rather than seen as having a failing.

In truth, he is a very natural adapter, a broad-centered man, deeply aware of others. He sees the commonality between different faiths as a positive, not a negative. He admires the Orthodox Church, and has made regular spiritual retreats to stay in the monasteries of Mount Athos, the Greek republic run by two thousand monks.

He is a practicing Anglican. Indeed, those close to him say it is because he has read and thought so deeply about his own Christian heritage and is firmly rooted in it that he is able to engage with other religions.

During his visits around the country he makes sure he is balanced, visiting Sikh, Muslim, Hindu and Christian communities. He has studied the Koran in depth and has been a student of the Arabic language for years. He has also studied Judaism in depth.

He believes that both faiths have "a great deal in common" with Christianity. "The future surely lies in rediscovering the universal truths that dwell at the heart of these religions," he has said.

The prince's belief in interfaith dialogue has long been on his agenda. He believes wholeheartedly that talking openly and honestly can only help strengthen communities and understanding.

Clearly, our next Supreme Governor of the Church of England plans to do the job a little differently. He has tested the boundaries of his public role by attending Catholic masses, and and the ceremonies of Muslims and Hindus.

But his bid to build bridges has left some confused and his critics to point an accusatory finger, wrongly, suggesting a lack of commitment to being a Christian and to the Church of England. They could not be further from the truth.

Much of the doubt stems from Charles's admission of adultery during his marriage to Diana, Princess of Wales, and his divorce that followed.

His detractors even to this day seem hell-bent on destroying him over this.

It is also driven by his apparently telling biographer Dimbleby in the 1994 book Prince of Wales that he wanted to be seen as a "Defender of Faith" rather than "Defender of the Faith" when he ascends the throne.

That is NOT his position now.

When he is crowned, he will be crowned Defender of THE faith like his mother before him.

But as sovereign, Charles will want to demonstrate that he can set an example for the entire country to follow and the coronation – which is expected next year in the spring or summer follow his accession rather than the usual year or even longer – would be a perfect vehicle to do this.

It has been made clear to me that Charles will "absolutely" be named as Defender of the Faith when he is crowned king. But he will also demonstrate in his reign that he believes wholeheartedly in the importance of his connecting with all faiths of the subjects he will reign over.

There is no doubt that Charles's faith is all encompassing. His appreciation of other religions comes from his wealth of study and reading over many years of interest. He makes all British citizens feel they are part of the grand historical narrative.

The king, at 73, the oldest monarch to assume the throne, knows he is not blessed with that much time.

It is clear that in Charles we are blessed to have a future king of high intelligence and drive. He may not be an intellectual in an academic sense, but he is a deep-thinking, spiritual man, not cynical but intuitive and instinctive. He is sentimental, too, and perhaps overemotional at times; but he is somebody who cares very deeply about the world and environment we live in, today and for the future.

He may be born into huge wealth and privilege, but he has always tried his best to justify that good fortune by working to improve the lot of others.

He has a great love of the arts, too, of books, of Shakespeare, of J. K. Rowling's Harry Potter, of the Goons, of the poetry of Dylan Thomas, of the music of Bach, Hubert Parry and Leonard Cohen, and of the classical architecture of Rome and Christopher Wren.

Fundamentally a decent man of integrity and honor who has always tried to put duty before himself.

Near Church House, after the cortège procession from Buckingham Palace to Westminster Hall I was getting a taxi, when I spotted Sir Nicholas Soames, Sir Winston Churchill's grandson and a long-term friend of Charles.

"How did you think it went?" I asked him.

"Brilliant," he replied, "The royal family were brilliant. The king was immaculate." I couldn't agree more.

Robert Jobson is an ABC News royals contributor, the author of "Charles: Our Future King" and the author of the upcoming book "Charles III - Our King." The opinions expressed in this story are not those of ABC News.