The best medicine for Charles? Long walks at Birkhall, an end to his ban on lunch and a daily dose of celebrated it laughter, courtesy of Queen Camilla

Sitting on a bench in an eco-sanctuary, Charles is inspecting a reptile squatting in his hands. The world's media surrounds him. But a passing bumblebee fancies some of the global limelight. It lands on Charles's lap – perilously close to the then Prince's crown jewels, causing an understandable yelp of concern.

It's a PR pratfall that would keep plenty of royal press secretaries awake at night. But sat next to Charles is Camilla, a past master in defusing many a princely timebomb, using the best tool at her disposal: humour.

The then Duchess of Cornwall is consumed with giggles and the laughter proves infectious, spreading among the photographers and reporters and finally to Charles – and in the hubbub the bee buzzes off.

An inconsequential vignette from a 2015 royal tour perhaps, but one that reflects an essential facet of the King and Queen's relationship and how they cope with problems large or small.

Deprived of glad royal tidings of late, the news that the King is returning to public duties came as much-needed balm, both to the hurting House of Windsor and the nation.

At Charles side is Camilla, a master of defusing many a timebomb with the best tool at her disposal: humour

The King and Queen Camilla will visit a csncer treatment centre on Tuesday, and the pair plan to host a State Visit of Japan in late Jute

After treatment for an unspecified cancer, the King, on doctors' advice, can attend events where he will meet people both indoors and outdoors. He and Camilla will visit a cancer treatment centre on Tuesday, while a State Visit from Japan is planned for late June.

It will not be 'a full summer programme', but doctors are 'sufficiently pleased with the progress made so far' and 'remain positive'.

To mark the announcement, Buckingham Palace issued a new photograph of the King and Queen, arms entwined and grins wide, taken in the palace's garden the morning after their 19th wedding anniversary this month.

If an ebullient picture could paint a thousand words... for it is the monarch, eyes crinkling, looking longingly at his consort, rather than the other way around.

Camilla, meanwhile, holds her gaze outward, to the photographer, symbolically encapsulating the duel roles Her Majesty has played over the past few months. At 76, she has taken on more than a dozen extra engagements to keep the royal show on the road.

But it is the support she's offered her husband in private moments of anguish that could prove a greater gift to the King – and the Firm.

Nobody can chase away shadows – and bees – like the Queen, whose unerring knack of summoning the right quip at the right time never fails to lift her gloom-prone husband. Sometimes all that's needed to set him off is a wry smile. She finds humour everywhere.

True, the King has drawn comfort from other sources – steadfast public support, for instance. But as a source says: 'Laughter is the key. They've got a very strong bond and a fantastic sense of humour.'

Since their early courtship, insiders say Camilla has been adept at 'keeping his spirits up', and – as noted by Mail writer and royal biographer Robert Hardman – has continued to 'inject a remedial note of levity' over the years.

Delighted photographers have captured the pair in giggles on several occasions.

In 2010, the couple laughed uncontrollably during an eccentric performance featuring a 'cat organ' at a festival in the gardens of Clarence House.

Although Charles will not have a 'full summer programme', doctors are pleased with the progress he has made so far since his cancer treatment

The black-tied musician before them squeezed a row of toy cats, each emitting squeaks of varying pitches – and all a helpless Charles could do was to dab his eyes.

Insiders also fondly remember Camilla's cheeky interjection at last year's Sandringham Flower Show, when she broke out in peals of laughter while examining a selection of pies.

'That looks just like my husband,' she joked, beckoning aides towards an anthropomorphic bake with oversized ears and a crown.

Not satisfied, Camilla pulled the King away from a serious chat with the show chairman to see 'a very, very nice pastry'. As anticipated, Charles guffawed loudly. 'It's an artwork, I think,' he said.

That first summer as King and Queen seems a world away from the events that would befall the Windsors. Following treatment for an enlarged prostate in January, the following month's announcement that King Charles had been diagnosed with a form of cancer and had started 'regular treatments' shocked the nation.

While a veil of privacy has been drawn over the King – and the Princess of Wales who is also undergoing cancer treatment – a brief window into the King's progress was provided when he attended church at St George's Chapel in Windsor on Easter Sunday.

Typically, Camilla kept close as he greeted crowds and laughed when a fan shouted out 'Camilla is 17 now' – causing momentary confusion, before she pointed to her pet Cavalier. Knowing his wife would see the funny side, Charles retorted: 'You'll need a new one!'

In recent weeks, gardening and walking near their beloved Highland retreat of Birkhall on the Balmoral estate, where they spent their honeymoon in 2005, has been a therapeutic shared interest.

With its tartan walls, carpets and big open fires, Birkhall feels more like a normal house than a royal residence and is, says one source, 'as close as it comes to being their marital home'. 

'This week at Birkhall has been particularly restorative for them both,' a source told The Mail on Sunday. 

'They've had close friends staying that they're deeply fond of, and the fresh air, the peace, and the freedom has been really good.' 

With impressive energy for a couple in their mid-seventies, Charles and Camilla spent much of last week walking in the grounds of the estate, unfazed by the wildly contrasting conditions.

'Mixed weather doesn't stop them,' said a source. 'It's been a really special time, coming in the wake of their wedding anniversary and reflecting on the anniversary of the Coronation.'

Gardening is another shared hobby at Birkhall, and something Camilla has described as 'the most relaxing thing in the world'.

The vegetable patch at 'Royal Deeside' grows simple fodder of peas, beans, spinach and potatoes, but also fennel, fraises des bois, sweet williams and dahlias.

It's a passion they retreated to during the pandemic and continue to indulge.

'My husband is an excellent gardener, and we're quite competitive about our fruit and vegetables,' Camilla has said in an interview.

While they have different tastes, the couple are also both voracious readers. Charles has a well-documented love of Shakespeare, while Camilla's book club suggestions reveal a love of thrillers and romance novels. 

Like walking and gardening, reading is a hobby Camilla strongly believes has health benefits. Last month, she endorsed research that said five minutes of reading a day was as valuable to health and wellbeing as walking 10,000 steps and eating five portions of fruit and veg.

Camilla has reportedly persuaded the King to resume having a lunch - something he gave up for Lent many years ago - to help keep his strength up

Following treatment for an enlarged prostate in January, the following month's announcement that King Charles had been diagnosed with a form of cancer and had started 'regular treatments' shocked the nation

'Just as we always suspected, books are good for us – and now science is proving us right,' she said at an engagement at Clarence House to mark the third anniversary of her book club.

The Queen has also reportedly persuaded Charles to have a midday meal during his cancer treatment to keep his strength up.

According to the royal biographer Ingrid Seward, writing in Majesty magazine, Camilla has impressed upon the King that it would be better to eat some lunch, 'however small'. 

It marks a significant change for Charles, who gave up his midday meal for Lent many years ago. This pattern of fasting strained his aides over the years, who learned to have a big breakfast when working with the King.

One former bodyguard even used to hide snacks in his jacket to snuffle them quickly when Charles wasn't looking.

As one source says: 'The Queen has been taking the closest possible care of the King.

'She has balanced being his chief supporter and carer, and being very protective of him, at the same time as having a very public role and taking on a greater share of formal duties. The Queen has undertaken both of those roles with dedication, devotion and relentless good cheer.'

But as he prepares for his busier schedule – with plans afoot for Trooping the Colour, Royal Ascot and Buckingham Palace garden parties (though the Palace is keen to stress that nothing is confirmed) – those who once held Camilla in high disdain, who considered her a threat to the monarchy's stability, should reflect that the nation owes her a debt.