The close relationship between King Charles and his daughter-in-law Kate Middleton appears to have become even closer, according to a body language expert.

Charles, 75, and Kate, 42, were reunited on the Buckingham Palace balcony today for the first time since they both began cancer treatment.

The Princess of Wales joined other members of the Royal Family to watch a spectacular flypast by the RAF as she made a triumphant return to public life at Trooping the Colour.

According to Judi James, during their balcony appearance, the two royals showed behaviour that was consistent with ‘a series of “reward” rituals that spoke volumes about family bonds and relationships behind the scenes’.

It has long been thought that the King and the Princess of Wales are close thanks to their shared interests in the arts, among other reasons.

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According to body language expert Judi James, Kate leaning in towards Charles showed her confidence, as well as ‘placing her in a supportive role’ with the King

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The body language expert also noted that the two royals enjoyed ’bouts of animated conversation that included eye contact and laughter’

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King Charles made the Princess of Wales the ‘centre of attention’ by standing next to her, said Judi James, who explained that this signalled ‘both how much she is cherished and how grateful he was at her attendance today’ (pictured L-R: Prince George; Prince William; Prince Louis; Princess Charlotte; the Princess of Wales, King Charles and Queen Camilla)

But many royal watchers say that after both being diagnosed with cancer, Charles and Kate have enjoyed a deeper bond.

Judi told FEMAIL: ‘Charles has always had an increasingly special relationship with Kate, who he has grown to trust and delight in.

‘Here though, that relationship was highlighted to illustrate how those bonds have only deepened and enriched by their bonds of empathy created by their illnesses.’

In a departure from last year, when King Charles stood next to his heir Prince William, 41, this year, he stood next to Kate.

This was significant, according to Judi, as she explained: ‘Charles made Kate his centre of attention to signal both how much she is cherished and how grateful he was at her attendance today.’

And it wasn’t just where they were standing that stood out: the way the two royals interacted spoke volumes about the relationship, according to Judi.

‘Kate was placed beside her father-in-law and the pair engaged in some bouts of animated conversation that included eye contact and laughter,’ she said.

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Members of the Royal Family watch the flypast from the Buckingham Palace balcony today

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Members of the Royal Family watch the flypast from the Buckingham Palace balcony today

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(From left) Prince George, Prince William, Prince Louis, Kate, Princess Charlotte, King Charles III, Queen Camilla, Sophie, Prince Edward, Lady Louise Windsor and Princess Anne today

‘At one point Camilla even moved to speak to her husband but his head was turned towards Kate for their chat.’

These interactions also showed Kate’s confidence, Judi said, describing it as ‘telling’ that ‘Kate lent to instigate their first conversation’. And the context of royal protocol made the move more significant.

As Judi explained: ‘The pecking orders on the balcony can be quite strict but Kate instigating the conversation showed not just confidence but it seemed to place her in a supportive role with Charles.’

While chatting, the pair were both seen smiling and laughing. Judi noted that ‘Charles did appear to appreciate the way [Kate] made him laugh, too’.

The huge crowds that had gathered today to catch a glimpse of the royals erupted when Kate stepped out onto the balcony.

And they continued to show their support during the national anthem. According to Judi: ‘Towards the end of the anthem, [the king] looked tearful at the support he and his daughter-in-law were receiving.’

The Royal Family came together to watch the spectacular flypast by the RAF, which was met with cheers from the crowds below.

It began as senior royals came out onto the balcony – with Charles and Camilla followed by Kate and William and their children George, Charlotte and Louis.

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William and Kate with their children next to Charles and Camilla at Buckingham Palace today

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Prince Louis, the Princess of Wales and Charlotte on the Buckingham Palace balcony today

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King Charles, Queen Camilla and Sophie, Duchess of Edinburgh at Buckingham Palace today

They were joined by the Duke and Duchess of Edinburgh, with the family smiling and waving to crowds before standing proudly as the national anthem was played.

Kate’s appearance had been in doubt after she missed the final Trooping rehearsal last weekend, with confirmation that she would attend only given at 6pm yesterday.

But with the King also suffering from cancer, today’s spectacle of military pomp and pageantry became a symbolic statement by the monarchy after much uncertainty.

Scotland Yard had a ‘substantial’ policing operation in place, with anti-monarchy group Republic allowed to protest but banned from using amplified sound.

Hundreds of Metropolitan Police officers were deployed on the ceremonial route to ensure the safety and security of those watching, with tens of thousands gathered.

Earlier, the 42-year-old Princess of Wales beamed and waved as she and her three children, Prince George, Princess Charlotte and Prince Louis, were cheered by crowds on The Mall in a carriage procession for the Trooping the Colour ceremony.

Kate was surrounded by other members of the family – with her husband Prince William , Colonel of the Welsh Guards, on horseback, along with Princess Anne , Colonel of the Blues and Royals, and Prince Edward , Colonel of the Scots Guards.

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(From left) Prince George, Prince William, Prince Louis, Kate, Princess Charlotte, King Charles III, Queen Camilla, Sophie, Prince Edward, Lady Louise Windsor and Princess Anne today

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King Charles III and Queen Camilla during Trooping the Colour at Buckingham Palace today

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William and Kate with their children next to Charles and Camilla at Buckingham Palace today

After spending much of the year coming to terms with the diagnosis and receiving ongoing chemotherapy, Kate looked relaxed as she travelled along one of London’s most famous thoroughfares with her family in the glass state coach.

The family were first seen arriving at Buckingham Palace in a car at 10am, with George sitting between Kate and William, and Charlotte and Louis opposite.

King Charles III also rode in a carriage with Queen Camilla, a departure from last year because of his illness, and he inspected the officers and guardsmen on Horse Guards Parade in Whitehall from the coach rather than from a horse.

Trooping the Colour is a social as well as a ceremonial occasion and the stands overlooking the parade ground were filled with about 8,000 spouses, girlfriends and parents of the guardsmen and officers on parade.

It featured more than 1,250 soldiers, and hundreds of Guardsmen were lined up on the parade ground waiting to be inspected by the King from his carriage with Camilla, Colonel of the Grenadier Guards, and joined by the mounted royal Colonels.

The colour, or regimental flag, that was trooped WAS the King’s Colour of number 9 company, Irish Guards.

When the royal carriages finally came to a stop Louis was the first to leave, followed by his elder brother George and sister Charlotte.

Finally, Kate stepped down wearing wearing a Jenny Packham dress, hat by Philip Treacy and the Irish Guards Regimental Brooch, as she is the regiment’s Colonel.

When the inspection of the Guardsmen in their scarlet tunics and bearskins began, the King cast his eye over the servicemen who are fighting soldiers when not performing ceremonial duties.

Sat beside him in the carriage was the Queen who wore a pale green silk crepe dress and coat by Anna Valentine, Philip Tracey hat and her Grenadier Guards military brooch.

During the pageantry the colour was first trooped through the ranks of soldiers before the guardsmen marched past the King, first in slow then in quick time with the King acknowledging the command of ‘eyes right’ with a salute.

For the first time in more than 100 years, soldiers on parade were allowed to have beards.

The rule change, which applies across the Army, was approved by the King earlier this year after facial hair was only allowed for religious, medical or role specific reasons.