Harry's allegations are not just about a royal fist fight – but the very real dangers of hereditary power | Gaby Hinsliff

The personal is political when resentment is baked into a monarchy whose instinct is to protect the heir at all costs

When my younger sister was very small, I once pushed her down the stairs. Fortunately, she was still small enough to bounce. But it was the beginning, not the end, of the fighting. We pinched and slapped in the back of the car on long interminable journeys, over a fraction of an inch invasion into each other's elbow space. We scrapped over toys and games and who got the biggest share of pudding; then over clothes and boys and who was most popular at school (all right, it was her). We fought like all siblings fight and I can't even remember now what most of it was about, but deep down it was probably the thing most sibling fights are really about, namely who is the most loved. Luckily in our family it was never obvious who was the favourite, which may help explain why these days we love each other to death; why the older we get, the closer we have become, through the years of bringing up our own children and now into the years of looking after our parents. But as I said, we were lucky. Prince William and Prince Harry have been less so, which may explain why - according to the latter's new book, Spare, a grimly revealing title if ever there was one - three years ago the brothers came to blows even as full-grown men.

The fight was ostensibly about Harry's wife, Meghan, and he writes angrily about his older brother calling her difficult", rude" and abrasive", echoing the whispers beginning to circulate about her in parts of the press. But it seemingly escalated violently after Harry accused William of acting like an heir: the chosen one, around whom everything else seemingly revolves. There isn't a sibling alive who won't, on some level, recognise that feeling. But the twist in this case is that resentment is inexorably baked into a hereditary monarchy from birth. Its strength but also its weakness is that it exercises power through a family, with all the primordial and potentially destructive emotions that entails.

Gaby Hinsliff is a Guardian columnist