The father of one of my RAF student helicopter pilots was an RAF squadron commander at the time. My protegee became a pilot on that same squadron, when "Dad" was in charge. He later surpassed his father's rank by quite a long way (and mine by even more). Nepotism/favouritism? Definitely not; it must have been a genetic trait. Or, of course, something to do with my training....
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But I was a mere direct entrant pilot - there was no private schooling or uni education and therefore no Cranwell for me. I came from what could be described as a humble working class background; no-one in my family had aviation connections and were about as far from "royal" as one could be.
But as far as the true royals being allowed into the armed services, Good on them; as far as I'm concerned it gives them the credibility they need and deserve and the present generation seem to be good at it.
They can't help their birthright / family heritage any more than anyone else can. To try to belittle them out of what can only be seen as some sort of twisted jealousy says more than enough about those doing so.