His full title is Charles the Third, by the Grace of God of the United Kingdom of Great Britain and Northern Ireland and of His other Realms and Territories, King, Head of the Commonwealth, Defender of the Faith.

To his grandchildren, however, he is just known affectionately as ‘Grandpa Wales’. While much has been written — not all, it has to be said, complimentary — about the King’s role as a father over the years, it is his unbridled enthusiasm as a grandfather that has shown Charles in a softer new light.

An enthusiasm that explains why, despite the family’s personal difficulties, the Prince and Princess of Wales were so keen that their children, George, ten, Charlotte, nine, and Louis, six, joined their ‘GW’ at Trooping the Colour on Saturday.

No major royal event would be complete without little Louis’s hilarious antics, Charlotte’s sisterly efforts to contain him and George’s endearing earnestness as the slightly more self-conscious older brother. But serious illness also has a habit of making us pull our loved ones even closer, and the Royal Family is no different.

In order for the youngsters to be there and play a full role — riding in a carriage on The Mall, watching proceedings on Horse Guards and joining the family ‘balcony moment’ — Mummy needed to be there too to keep the ‘kiddies’ (as she calls her young brood) in check as Papa was on horseback.

For Kate, there was also a determination to support the father-in-law she has become increasingly close to over the years and with whom she now shares the unenviable bond of a serious health battle. In recent years the King has become a central part of William, Kate and their young family’s lives — a relationship emphasised by the lack of personal contact with Harry and Meghan’s two, Archie, five, and three-year-old Lilibet.

He has only met his youngest granddaughter in person once since she was born, and Archie barely a handful of times.

Recently, it was suggested that the King was unhappy with the situation and ‘keener than ever’ to build a relationship with them that wasn’t just confined to video calls to California. The story was not universally welcomed as it put Buckingham Palace in an impossible position: those close to the King genuinely never speak about the Sus𝑠e𝑥es’ children to avoid inflaming transatlantic tensions, but to deny it would be to suggest that the King doesn’t want greater contact with them — which clearly isn’t true at all.

And the situation is particularly complicated because of Harry’s repeated attacks on his father and family, his dogged insistence in the UK courts that he isn’t safe bringing his family to the UK, plus Charles’s inability to travel to the U.S. because of his health issues and responsibilities.

When I asked a well-placed source whether Harry could bring his children to see the King at Balmoral this summer as a compromise, the answer was a resounding snort. Read into that what you will. His relationship with his other three grandchildren is in a far better place.

The family’s relocation to Windsor, where they live in Adelaide Cottage in Windsor Great Park, along with the King’s decision to spend more time at the castle, has given him the chance to see more of the little Waleses. One close friend says: ‘He cherishes being a grandfather and enjoys enormously the time he spends with them. He loves playing with them in the garden and reading to them.’

I’m told that the King has even named an area he has created at his Scottish home of Birkhall ‘Prince George’s Wood’.

‘While people don’t see often him with his grandchildren that much because most of those moments happen behind closed doors, I know he is very careful to ensure he makes time for them in his busy schedule,’ the close friend says.

He is, another source tells me, ‘doting in his own way’.

It wasn’t always so harmonious.I have previously revealed how, when Charlotte was born in 2015, Charles and Camilla headed off to his Highgrove residence in Gloucestershire after William had told them they would not be seeing visitors over the Bank Holiday weekend. However, on the Sunday, word slipped out that Carole and Mike Middleton were on their way to Kensington Palace to see their new grandchild.

Charles then had to undertake a dash down to London so that he wasn’t seen as uncaring.

Things couldn’t be more different today, and people have come to see an endearing new side to the King: whether that be an affectionate moment with a smiling Charlotte on the balcony on Saturday, bouncing a bored Louis on his lap at Queen Elizabeth’s Platinum Jubilee celebrations, or cuddling Prince George in a rare family photograph.

He’s also talked about speaking to his grandchildren during the Covid lockdowns on videos calls, revealing how tough he found it not to be able to reach out and give them a hug.

‘I think that was a bit of a revelation to some and people have started to see him for the grandfather figure that those close to His Majesty already know him to be,’ says another source.

He has an equally close relationship with his wife’s five grandchildren. In an exclusive interview with me to mark her 70th birthday in 2017, the then Duchess of Cornwall revealed how much he doted on her grandchildren.

For many years, I am told, King Charles also held a big party at Clarence House each summer for family and close friends, with children running around his flower beds and shrieking.

Those treasured moments may be somewhat more difficult to organise now, given his new responsibilities as sovereign. But there is no doubt that among the many grand titles he holds, the simple nickname of Grandpa Wales is treasured most dearly.