The other Royal celebration: Welcome to Prince Archie's fourth …

There are two Windsor males to celebrate this week - one will be on the receiving end of a tad more pomp and ceremony than the other, but both will be basking in the limelight of a meticulously planned party. Yes, it's Prince Archie's fourth birthday, and the eldest child of Montecito's best-connected couple is likely to have an event with a curated guest list and thoughtfully planned food and entertainment. Just like his grandfather, King Charles.

After all, this birthday is the reason Meghan isn't coming to the Coronation, and why Harry is flying home three hours after the ceremony ends (the time difference means he could catch the tail end of a late-afternoon celebration). Prince Archie Harrison Mountbatten-Windsor may be seventh in line to the British throne and the grandchild of the reigning monarch, but he apparently speaks with a thick American accent. According to sources close to the couple, he is "thriving" in his new Californian life, he loves running on the beach and playing in his park-sized "backyard".

In many ways, it's a charmed life: sun, acres of grounds to roam in, chickens, dogs (Prince Harry has been spotted with a new Labrador puppy), a swimming pool and a tennis court, as well as the sea a 10-minute drive away. Unlike his British cousins - who he barely knows, having last met them in early 2020 when he had not yet turned one - Archie wears the Californian uniform of jeans, cotton trousers or shorts, and T-shirts, usually with a sunhat plonked on his russet-coloured curls. Now he is a bit older, school - or rather kindergarten - beckons.

According to a local journalist, All Saints by the Sea is the most in demand pre-school in the area and is a five-minute drive from the Duke and Duchess of Sussex's mansion. Another option is The Waldorf School of Santa Barbara, which is "committed to providing a healthy, broad, reverent education that honours the head, heart, hands - the whole - of the child".

Phew. Although this "thoughtful" language might give us an indication of what to expect from today's party, not much can touch a coronation in the planning stakes - but birthdays for California's most privileged sprogs can come close.

First up, the guest list. The Duchess's mother Doria Ragland is likely to be the only family member in attendance (what with her ex-husband being persona non-grata and Prince Harry's relatives elsewhere engaged). Hands-on grandmother Doria was filmed in the Netflix documentary Harry & Meghan, laughing and playing with Archie and his toy car.

But other than her, Archie barely knows his family. Courtiers have spoken about King Charles's sadness at having only met his grandson a handful of times - twice before the Sussexes left Britain, and there was an emotional reunion with the little boy at last year's Jubilee. As for the Prince and Princess of Wales, frosty relations aren't extended to the children, and the couple is likely to send Archie a birthday present - despite having not seen him since early 2020 at a charity polo match.

In fact, Princess Diana might be his only British relative looking on: a documentary clip showed the Duchess holding Archie up to the late Princess's picture, cooing, "Hey Grandma. That's your grandma Diana." Meanwhile, the people we believe to be Archie's godparents - Charlie van Straubenzee, Tiggy Pettifer (once Harry's nanny), and former Welsh Guards officer Mark Dyer - will also be absent.

The first two have been invited to the Coronation, and sadly, Dyer is battling stomach cancer. Despite the lack of family, plenty of Archie's friends, their parents and any local big names with children a similar age are expected. "In Montecito, celebrities are royalty," says LA-based author Lisa Gache, who teaches children's etiquette classes at the high-end Montecito Club. "It's Oprah and Ellen but also Serena Williams - pregnant with her second child - and Katy Perry and Orlando Bloom, whose daughter Daisy is a year younger than Archie.

If there's any celebrity with a child the same age, it's safe to assume they'll be invited."

As for the party itself well, in Montecito it can go either way ... On one hand, there are wildly extravagant children's parties where six-figure spending is the norm. Think 50ft-wide painted backdrops, food trucks, Ferris wheels and vast balloon garlands.

"People here aren't embarrassed about spending serious money on kids' parties - nowadays that over-the-top look is applauded," said Leesa Zelken, the founder of LA-based party planner Send in the Clowns. "Balloons look so great on Instagram - my clients regularly have a balloon budget of around £10,000." Zelken has done everything from installing ice-skating rinks in the garden of a Beverly Hills house to training actors to recreate classic Disney films. And if she were asked to organise the young Prince's birthday?

"I would lean into something all-American," she says. "They have embraced being here - the party should reflect that. It's also the perfect time of year for a fair with hot dogs and picnic tables. Things that feel very celebratory of their new life, not their old one."

On the other hand, Montecito is a slightly different beast to its neighbour to the south: ultra-monied, but not quite so brash as Los Angeles. In the Netflix documentary, Archie's first birthday party was a modest affair: a few blow-up balloons and a charmingly homemade wonky cake covered in raspberries. Yes, that birthday was during lockdown, but sources say the Duchess plans another "intimate" celebration and to once again make a cake, this year using lemons from her garden's tree.

"The residents there tend to come from older money, and that means a different approach," says Gache. "There is wonderful access to wealth, but at the same time, there is a down to earthness and therefore not quite such a desire to put on ultra-lavish affairs."

Gache imagines there will certainly be a theme, games in the garden and various entertainers. Although in ultra-woke California, asking for Cinderella could get you cancelled. "I went to one Montecito party where the parents were appalled to find an actress dressed up as a princess," says a local source. "Apparently their daughters were being taught a 'narrow version of femininity'. Still, the little girls loved it."

If Archie wants a superhero party, he may have to accept that Safespace and Snowflake - the two "thoughtful" heroes Marvel introduced in 2020 - will be guests of honour. Party paraphernalia has also always been comically ethical and progressive in LA. And it doesn't come cheap either - single-use plastic is likely to be banned in favour of wooden cutlery and plates, while party favours (in biodegradable goody bags) will carry ethically sourced toys from companies like Jessica Alba's Honest, which promotes "clean living for mamas and babies".

"They are also fixated with safety," says the British source. "There are emails in advance about making sure there is no gluten on the premises, even if no children are gluten-intolerant." Children's parties are rarely the smorgasbord of sugary treats they are in Britain. "In this neck of the woods, we have so many children who are vegetarian or keto or paleo, and they need to be aware of that," says Gache. As for the adults - there will be lots of salads, and not much else (and certainly not a whiff of sauv blanc). "Alcohol is frowned upon for kids' parties in Montecito," says Gache. "The Duke and Duchess are conscious of mental health and raising kids in an appropriate manner, I doubt they would serve it."

"There's no chance of having a glass of Champagne," agrees the British source. "It's all rather twee and an excuse to show off your credentials as a parent and a human being rather than relax and have some fun in the sun." Still, for the children, life in Montecito is about as good as it gets: carnival-like birthday parties, child-led learning (which essentially means no discipline) and afternoons on the beach. One day soon, Archie's buttoned-up cousins across the pond may start looking at their American relatives with a touch of envy.

If they ever meet again, that is...