Those close to William say this is the most publicly vulnerable we have seen him

Over a pint of cider, with his pet dog Orla by his feet, Prince William sets out, in one sentence, his manifesto for the monarchy: "Change is on my agenda." The setting and the choice of platform for it, a travel series with a Hollywood actor, could not feel more unexpected, and we are told it wasn't necessarily planned to happen this way.

A free-flowing conversation is how it was described to me. And the result was the most personal and open interview, on topics that would usually be considered off limits.

Those close to William would say it's the most publicly vulnerable we have seen him. It has to be said, a lot of it does not entirely come as a surprise to those of us who follow the Prince of Wales on a weekly basis.

We have heard before that he wants to carry out his duties with a "smaller R in the royal" and focus on social purpose and empathetic leadership. We have been briefed that he wants to put his children and wife first, and that is why both the prince and princess arrange their working visits around school hours and school holidays.

And we have seen, ever since the children were born, how protecting them is his priority. But this is the first time we have heard a lot of this on camera from the man himself.

So what does "change" really mean? Fewer garden parties, ditching the ermine robes, less ribbon cutting and plaque unveiling? That is all less clear, but just the fact that we have now seen William actually say it is hugely significant. Why? Well, you have to remember this is a family who don't like to talk publicly about "transition".

Remember that death and mourning come hand in hand with a change of reign. And there's the public reaction to talking about it.

In the past, King Charles, as Prince of Wales, was often criticised for pushing an agenda of change on a whole range of issues, but when asked about the kind of monarch he would be, he very clearly shot down any suggestions that he would "meddle". There is so much public goodwill towards his son and heir, I am not sure that William's thoughts will attract the same kind of critique.

Although some in newsrooms may question whether his choice of interviewee and TV show highlights a reluctance to be challenged or questioned fully on his ideas and the way he works now. No, William is not signalling that he will politically interfere, but will his thoughts for the future of the monarchy be seismic? Evolution, rather than revolution, is how it was once described to me.

He still makes clear that he respects tradition, but as sources told me, he is not afraid to ask why certain things happen, and question if it's really fit for now. We have seen it with his approach to the Duchy of Cornwall.

And apparently, the worst answer you can give him is "well we've always done it that way". In the programme, he talks of missing Queen Elizabeth and Prince Philip, and I suspect his grandfather would be proud, as a man who ruffled palace feathers himself, reorganising royal estates, installing telephones and removing the footmen who used to run messages.

They have wanted to be known as a family of modernisers. Importantly, now does feel like a safe time for William to publicly articulate what is to come.

His father, while still undergoing cancer treatment, could not be busier or, it seems, more determined to make his own mark as monarch. His son, meanwhile, can for now focus on balancing being the best father he can, with the expectations of being heir, knowing that one day destiny means he too will have to embrace change..