If the Duke of Sussex uses his 40th birthday to reflect on the past decade, he’ll have plenty to ponder.

Prince Harry will celebrate privately on Sunday, with his wife and children, in Montecito, California before heading off on a break with friends.

Messages came from the Royal Family, who haven’t publicly acknowledged Prince Harry’s birthday for two years.

First, a social media post from Buckingham Palace wishing him “a very happy 40th birthday".

Then, just over an hour later, the same message was reposted by the accounts of the Prince and Princess of Wales. The posts didn’t come with personal messages but the fact they were there at all is interesting.

After a tumultuous 10 years - the question is whether the next decade will be a smoother ride for Harry.

It’s not easy to answer. As always with the Duke and the Duchess of Sussex, views are polarised and entrenched.

I first met Prince Harry in the months before his 30th birthday. He's now told the BBC it was a period in his life when he felt “anxious”.

Back then, we chatted about travelling by tube - something he told me he’d never done. He joked with a BBC colleague I was with. And he talked about his plans for the future away from the comfort and shelter the Army had provided.

I remember walking home thinking about how restless Prince Harry had seemed.

Definitely chatty and entertaining. Enthusiastic and energised. But also restless.

I last met Prince Harry in May of this year. Now he's a husband, father, ex-soldier, former working member of the Royal Family and resident of California. The chat about the London Underground felt like a lifetime ago.

We spent around an hour filming with him at a central London hotel where we watched him lead the games at a children’s party for one of his charities. He couldn’t resist joining in and was an impressive winner of the “Who could eat a strawberry lace the fastest” competition.

In many ways, we were watching the Harry of old. He was informal and fun. He mucked in and chatted to just about everyone.

In the noise of leaving royal life behind, this version of Prince Harry hasn’t been on show as often.

In recent weeks, there have been suggestions that we might see a bit more of Prince Harry in UK, that he was feeling the pull of his former home and reaching out to old friends and those he’d previously worked with about spending more time here.

But there is little evidence to back up those rumours.

One friend of Harry told me a return to the UK wasn’t on the cards. “Why would he give up everything he’s achieved there to return here? His life is now in America.”

But those close to him say he’d like to come over more regularly to work with the charities and organisations he supports.

Security is the problem. The row with the Home Office about the level of police protection he gets in the UK is ongoing.

The bottom line is Harry doesn’t feel his safety is guaranteed in the UK.

When he was here earlier in the year, he was offered a place to stay at a royal residence in London.

He turned it down believing his royal location would become public knowledge, attract media attention and make his movements around London difficult and risky.

Instead, he stayed under the radar, based with his team in a London hotel.

The physical distance between the prince and some of the organisations he works with has meant relationships have changed.

But Harry’s team from his Archewell Foundation and many of the projects I talked to said the prince was an active and engaged partner, even if he was thousands of miles away.

Later this month, he’ll be in New York working with a number of organisations including the Halo Trust, which helps clear landmines and rebuild communities in areas of conflict.

After Russia invaded Ukraine in 2022, the Halo Trust set up a call between Harry and some of the organisation’s staff in Donbas, eastern Ukraine.

“This wasn’t a quick how are you doing, thinking of you. It was a long conversation and it really meant a lot to them,” said Louise Vaughan from the Halo Trust.

• Listen: Prince Harry at 40 - time to reconcile?

Back in Montecito, California, Harry’s life moves between the routine of the school run to hanging out with A-list friends.

There are occasional photos published of Harry walking the dogs or Meghan having lunch with friends but with their own security team they have been able to live a relatively normal existence.

Just last weekend, Harry and Meghan were at the opening of a new bookshop in the town.

On the surface it appeared a relatively modest affair until you looked at the guest list – Oprah Winfrey, Ellen de Generes and her wife Portia de Rossi were there too.

The Montecito circle is exclusive, discreet and rich. It’s provided a lavish refuge for Harry and Meghan and given them a degree of protection from the public spotlight.

But the Duke needs to continue making money. Maintaining their home and security detail isn’t cheap.

The multi-million dollar deal with Netflix remains in place where other lucrative contracts have ended.

In December comes “Polo” – a series looking at the “elite world of professional polo”. It is a sport loved by generations of royals. Harry is the executive producer.

And in just weeks, the paperback version of Harry’s memoir “Spare” will be published, after the hardback sold six million copies and became the fastest selling non-fiction book of all time.

Unusually for a memoir of this kind, the new paperback won’t have any updates or additional chapters. There will be no take on the Coronation which the prince attended; no insight into how difficult it has been with his father and sister-in-law unwell.

Is this an olive branch from Prince Harry? A recognition that the bombshells revealed in the first version of “Spare” caused so much damage that to say anything else, after a challenging few months for the Royal Family, would be unpalatable?

Maybe.

The state of the relationship between Prince Harry and his royal family still fascinates.

And there’s some evidence on the smallest of shifts in family relations.

News of the King’s cancer diagnosis brought Harry straight back to the UK to see his father in February.

He was here in the UK for 24 hours and only spent around half an hour with the King. It was a strangely short visit that many found hard to understand.

But the fact that Harry flew over and the King made time to see him suggested there was potential for a fix in that fractured relationship.

It is a different story, for now, with his brother.

The Prince of Wales and his younger sibling do not talk. There is anger, frustration and bitterness that show no sign of easing.

Harry’s TV interviews, book and public criticism of the Royal Family has been too much for his older brother and several other senior royals.

“I just can’t see a fix,” said a source who’d worked with William and Harry. “It’s been a long time now and they haven’t found a peace. Their lives are now very separate. It’s sad.”

As he reaches a milestone birthday, mending his broken family relationships will be complicated and slow. Some bonds feel like they could be beyond repair.

Prince Harry has made some life-changing choices over the past decade.

He has left behind the “anxious” and restless 30-year-old prince and replaced him with the 40-year-old royal outsider, “excited” about his next decade.