I used to take comfort in the idea that all things pass in time, now not so much. Probably because I realised that includes everyone I love, and myself!
I’ve no great love for the monarchy, but this is certainly the end of an era in British public life and likely in UK international relations - I can’t see the commonwealth nations welcoming King Charles as their new head of state.
And it is weird, there are some things you just never expect to change. I’m hardly a spring chicken, but Queen Elizabeth was not only there my entire life, but Queen far enough into the past before I was born to have interacted with historical figures (like Churchill).
I don't expect it's unusual for a monarch to be something of a philosopher though - they're somewhat inherently well-educated, thoughtful, devoting time to deep thought, etc. Less usual (in modern times anyway) is to hear their thoughts in public as we did while he was Prince of Wales; we'll see to what extent that continues - he has said he's 'not stupid' and that he recognises the role of sovereign is different. If I had to bet though, I imagine he does see a bit more room for public commentary than Elizabeth II made.