'Camille? She's a bloody brick: the Queen will be with Charles every step of the way. And their ability to laugh together will be needed more than ever during this health crisis, writes REBECCA ENGLISH

'Friendship, love and respect. That is what drives them,” a good friend of the King and Queen recently told me.

'They are very different people in many ways, but at the core you have two people who really love and respect each other and still laugh a lot. It's really sweet.'

It is a judgment emphasized by Annabel Elliot, Camilla's sister, who described them in a BBC interview last month as 'yin and yang' but as an extremely 'brilliant' team.

And that is why I have no doubt that Queen Camilla will be more of a rock for the King than ever in the coming difficult months.

Naturally, the disturbing news that her husband has been diagnosed with cancer will be a huge blow to Her Majesty.

From the moment they first fell in love in their early twenties, Charles and Camilla's lives have been inextricably linked.

While their story may not have been a conventional love story – the late Queen Elizabeth at one point feared that the couple's passion could spell the downfall of the monarchy – it is one that can ultimately be regarded as one of the most enduring of our time.

Their Majesties will celebrate their twentieth wedding anniversary next year, a milestone that many once thought utterly impossible.

But the Queen is also stoic – the definition of the British stiff upper lip – and someone who takes things very easily.

I'm sure her approach to this devastating news will be typically calm and pragmatic, and she will insist on being by her husband's side and supporting him every step of the way.

I can tell you that she was with him last night at Clarence House when he returned to London to begin outpatient hospital treatment.

And I am told that while she is understandably concerned and preparing to 'play an important role in supporting the King during his period of treatment', she plans to continue a full program of public duties at the same time.

That British stiff upper lip again.

“She's a fucking brick,” says a friend.

Ironically, in the early days of their marriage, it was Charles who protected Camilla the most because he knew the magnitude of what she had taken on to be by his side.

On their first official trip to the US after their wedding in 2005, I watched as the future king instinctively reached into the aisle of our plane and squeezed his wife's shaking hand as we took off, knowing how terrified she was of flying (although I also subsequently heard him shout during one particularly bumpy flight, “Honey, please don't hold me so hard!”)

But over the years, Camilla has blossomed, becoming increasingly confident under the often very cruel public spotlight and gaining admiration for her work ethic and confidence in taking on old-fashioned causes.

Of course, things haven't always gone smoothly.

Camilla's relationship with William and Harry has always been extremely complex.

But privately, William recognizes how happy Camilla has made their father and appreciates the fact that she never tried to interfere in their lives.

There is also admiration for the way she has zealously embraced royal duties at a time in her life when most people would be slowing down – without a peep of complaint.

'The King and Queen know what their role is, why they do it and what they want to achieve. She has become increasingly bold in the work she does, tackling difficult issues such as domestic violence but not stepping on any toes. They work well together and there is a lot of mutual trust,” the friend said.

The same band is also visible in private.

'They get along great, they share the same sense of humor and make each other laugh. They have the same interests: the countryside, walking, their dogs… and yes, the Queen also knows when to make a hasty retreat. She knows when to give him space,” another source added.

Although she strongly supports her husband's dedication to the causes he holds dear, Camilla also doesn't mind poking lovingly at that seriousness every now and then.

More than once over the years, I've caught her eye as her husband waxes lyrical about a cause close to his heart, a knowing smile on her lips and a mischievous glint in her eye.

During an official visit to Egypt several years ago, the entire royal entourage was forced to rough it somewhat in modest mud-brick houses because Charles was eager to visit an eco-friendly, electricity-free village.

His wife later confided to me, amid much amusing eye-rolling, that the lack of electrical outlets was “all well and good if you don't have to use a blooming hairdryer.”

But don't mistake her ability to sometimes laugh at the absurdities of the position she found herself in as a sign of casual disgust. Queen Camilla is fiercely loyal to 'her husband' – and woe betide anyone who disrespects him.

“It sounds so terribly cliché, but she truly respects her husband, his drive, his passion to change the world for the better,” says another confidante.

“She is his fiercest champion and no one should underestimate her loyalty to him. They come as a team. Disrespect him is at your peril.”

In all the years I have worked with her, I have never heard Camilla refer to her husband as anything other than 'His Royal Highness, the Prince, the King or His Majesty', even in private.

“She has enormous respect for her husband as a king, but also as a man, and for the institution of the monarchy,” another source added. “That's something Queen Elizabeth also came to admire.”

And a friend tells me that as Camilla becomes tolerant of her husband's idiosyncrasies, he is just as patient with hers.

“He has, how should I put it, brought a bit of discipline to her, er, somewhat disorganized routine,” they noted wryly, with a nod to Camilla's notorious sloppiness and previously rather “relaxed” attitude to life.

Of course there is friction every now and then.

The king can become irritable if his wife talks too much. She wishes he would go slower, just a touch.

But they are small, everyday marital disputes and the king is clearly grateful to have someone with whom to share this rather strange and sometimes lonely life.

You only had to see the smile of undisguised pride that lit up his face as he watched his wife walk out of Buckingham Palace in her coronation get-up last May to understand how much she means to him.

They still have separate homes: Camilla has Raymill in Wiltshire, bought as a single woman, where she lives an informal existence away from strict palace life, while Charles still loves the formality/informality of Highgrove in nearby Gloucestershire .

But they are still close, so confident in their relationship that they can just sit in a room and read, without saying a word – just the occasional smile.

Charles has also embraced Camilla's family like his own. He has a huge bond with her sister Annabel, who will provide a shoulder to cry on for her sister who lost her husband to a long-term illness a few days before the coronation last year.

And he adores her children, Tom and Laura, and her five grandchildren.

During an interview five years ago, Camilla told me how her husband was a brilliant storyteller, who regularly read to the children at bedtime, especially Harry Potter, and did all the different voices for them. They were always fascinated, she said.

It is a side of the King that few get to hear about.

Above all, there is laughter. The kind of painful, heart-wrenching laughter that makes you weak in the knees.

At royal engagements, you'll often see the couple literally crying over a shared joke, appearing again and again as they grab each other's attention – no mean feat after 18 years of marriage – especially when things don't go quite to plan.

Laughter is something they will need more than ever as a couple as they face the King's current health crisis.

And like everything in life, it is something they will tackle together, united.

King and queen, but more importantly, husband and wife.