Thank you for that recommendation, published 2010 and seemingly out of print, but I've ordered a second-hand copy.
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.
It starts with “this is a call to revolution…”
A philosopher king!