Is the King about to give Kate a promotion as she turns 42? And William and Kate could soon be handing out their own Royal Warrants to favorites like Lululemon…

As the birthdays pass – befitting a future queen, that is – the celebrations will be low-key. “They'll be in Windsor when the kids first go back to school, so it'll just be family,” a source says, almost apologetically. “But honestly, that's just the way she likes it.”

And who can blame the Princess of Wales for celebrating her 42nd birthday on Tuesday with jelly and ice cream at home with the kids instead of something more high-profile, after the whirlwind of recent months?

After all, it's been just over a year since the late Queen's death and Catherine's promotion to Princess of Wales. And it's an elevation, meaning there's now no buffer between her and William and the throne.

While William had to rise as the new Prince of Wales and Duke of Cornwall and take on a host of further responsibilities, the demands were also felt by his wife. And things are moving up a gear.

There is much talk in royal circles that King Charles might even seal his daughter-in-law's new position in the near future by appointing her Royal Lady of the Order of the Garter, the oldest and highest Order of Chivalry in Britain. Founded almost 700 years ago by Edward III, inspired by the stories of King Arthur and the bravery of his Knights of the Round Table.

The appointment, personally chosen by the monarch for her service to the crown or national life, would cement her seniority and place her alongside Queen Camilla, the Princess Royal, Princess Alexandra (and the Royal Knights, including her husband Prince William, Prince Edward , Prince Andrew and the Dukes of Kent and Gloucester).

Catherine normally watches the annual procession on Garter Day, in which the King and his knights and ladies walk from Windsor Castle to St George's Chapel, in their large velvet robes and ostrich-plumed bonnets, from the Galilee Porch of the chapel.

But many senior figures believe that after more than a decade of peerless royal service, she deserves a place in their own right.

There is also talk that the princess – and her husband – could be given the power to issue her own royal warrants for the first time.

Pressure is mounting on the king to decide which members of the family he should allow to award these sought-after decorations, a tradition that dates back to the Middle Ages and allows senior royal officials to allow companies that regularly award them supply goods or services to use their weapon.

Owning a Quality Mark, which can be displayed on their business premises, products, packaging, stationery, advertising and vehicles, brings enormous commercial compliments at home and abroad.

And while it is likely that the King will first issue some new royal warrants himself, and let Camilla do so for the first time, the prospect of warrants for the Princess of Wales would be welcome in many quarters.

Several existing holders I have spoken to believe that the value to British businesses of an official endorsement from the Princess of Wales is almost incalculable.

“It would be a huge boost for British industry,” said one. 'Interest would increase enormously, especially in the field of fashion and lifestyle.'

A royal source told me that the question of whether the Prince and Princess of Wales would be given the power to issue their own Royal Warrants was a 'grey area' and that the final decision lay with Buckingham Palace.

'They are aware of it. Hopefully something will happen sooner or later,” she added.

I'm also told that this year the Princess of Wales will undertake her first solo royal overseas visit in two years, the last of which will be to Denmark in February 2022.

Although nothing is in the diary yet, it's said to be something the princess is “actively thinking about”, in addition to a work trip to Rome with her husband this spring, which I exclusively revealed in the Mail last month, and has long been past.

Because while the Waleses are a formidable force together, a solo trip abroad would give Catherine the opportunity to spread her wings and better showcase the causes she is personally passionate about.

Her last official trip abroad, more than a year ago, was to Boston in support of her husband's Earthshot Prize awards.

Indeed, the princess's workload is something that often sparks debate – and can lead to complaints that she is not doing her best.

The annual review of royal engagements published last month (not official, but with which palace aides rarely disagreed) calculated that she performed just 134 engagements in the previous 12 months – about one every three days.

It's no doubt a fraction of what other royals have performed well into retirement age, including the King (516), Princess Anne (410) and even the 79-year-old Duke of Gloucester (190), and quietly noted a bit be on the low side.

However, this is something that worries those close to her, who emphasize that she and her husband have long made clear their desire to be more involved with a smaller number of charities, both in front of and behind the scenes.

Someone tells me, “What the court circulars don't show is the hours and hours it spends on the team that designs the programs you see in public.

'Like her husband, she is deeply involved in planning, which is not reflected in the number of assignments undertaken annually. It's annoying.'

Others point out that even as Princess of Wales, Catherine's priority remains her children: Prince George, 10, Princess Charlotte, eight, and five-year-old Prince Louis.

And if recent public engagements are anything to go by, she is successfully raising three well-adjusted young people, who are gently coming to terms with the enormous public interest in them.

The move to Windsor in 2022, where the family of five have settled comfortably into the decidedly cozy (by royal terms) four-bedroom Adelaide Cottage, has certainly helped them all adjust to their new status.

While the sad death of Queen Elizabeth in the autumn of that year – on the day the children entered Lambrook School – disrupted plans to spend more time with Gan-Gan, the move was 'good for them all,” says someone who knows them well.

There is a trampoline in the garden and the children can often be seen cycling around the Windsor estate with their parents.

William and Kate share the school run and are a noted cheerer on the sidelines of their children's sports matches – even queuing for the raffle at the recent Christmas market – and are admired by locals as 'a sweet little family '. Nevertheless, while the children are at school, Catherine has been working hard on a number of important initiatives, the fruits of which will soon be shared.

As always, her main priority is her passion to highlight the crucial early years of childhood and how our experiences between birth and the age of five influence us as adults.

At the beginning of this year, the Princess will make public the work of her 'business task force', which has been conducting research into the role the industry can play in child development.

And to be fair, it is to her great credit that just months into the project she has attracted the involvement of a number of major companies – Lego, IKEA, NatWest, Unilever, Avila, Deloitte, Co-op and Iceland.

She is an increasingly confident public performer – although far from the finished article – and is also keen to take on more of a 'social leadership' role, like her husband.

“She has always thought about long-term change, not short-term gain. There is no rush for an easy win,” said a source close to her.

You might even think that this has been Catherine's mantra for life.

And from the looks of it, such an instinctively pragmatic approach will serve her very well in this next phase of her extraordinary royal career.

But first: a little piece of birthday cake.