AN acquaintance of mine recently married into one of the world's royal families. Or rather, into a royal family in

exile. This proved interesting to observe. There is no one so grand as an ex-royal. The lack of a throne to sit upon, and a country to lord it over, only seem to increase the sense of self-importance.

My acquaintance, it turned out, was joining the dynasty on wildly unequal terms. Under sufferance, really. The parents would clearly have preferred an arranged marriage for their thoroughly modern children, but even royals are, after all, living in 1992. The real eye-opener was these exiles displayed not one shred of genuine interest in establishing friendly, courteous links with the newcomer's relatives or friends. They were simply of no consequence. They may as well not have existed. The arrogance was breathtaking. Royals, I concluded, really do imagine they are different from the rest of mankind.

The newcomer, while welcomed, was expected to obey arbitrary rules set down in stone by elderly people. Holidays were supposed always to take place in the same spot, with the children attending in rotation. A new home could be purchased only in an approved location.

I write this because the tensions this process engendered provided me with an insight into the even grander style of the House of Windsor, and some explanation for its marital disasters. It has been odd, returning home from holiday abroad, to catch up with the flood of reports of the Duchess of York's final disgrace, and the apparent taped evidence of the Princess of Wales's unhappiness. It all brilliantly illustrates the truth of Tolstoy's dictum in Anna Karenina, that while 'All happy families resemble one another, every unhappy family is unhappy in its own way'.

The image that particularly haunts me is of the Duke of York beaming broadly - first, when he is being driven to church at Balmoral, in the front seat of the family limousine, with his mother and father in the back seat; second, when he is pictured larking about on the golf course.

Perhaps he is feeling relieved at being shot of his troublesome wife's presence. But is he really so blameless? For one of the key things that has gone wrong for the Princess and the Duchess is that they married men who are deeply attached to their own family, who live in an unhealthy orbit around their mother, the Queen, and in the case of the Prince of Wales, his grandmother. Their wives are expected to live surrounded by their in-laws for large amounts of time. Both the Princess and the Duchess come from broken homes, and it is noticeable how little place their own families and mothers seem to play in their ordinary life.

Equally, when their marriages took place, it was noticeable that their own relatives looked exceedingly uneasy in the presence of the Windsor clan, even when one of them happened to be an earl. The Windsors do not give the impression of being a welcoming family. Incomers are expected to join on their terms.

It is here, surely, that the lesson for everyone lies. For marriages to work, and young families to prosper, there has to be a process of detachment. The new unit has to matter more to the man and woman concerned than their original families do. It has to become the main emotional focus of their lives, the first claim. It can be compromised by any number of things, including unfaithfulness. But without commitment, the relationship is unstable.

This process of detachment must also be recognised and accommodated by the couple's respective parents. A happy family has to be prepared to extend, change and accept new members, while loosening the emotional grip on grown-up sons and daughters.

Most people, I have noticed, hold an exclusive and limited view of who belongs within their family: in this the Queen is no different, just more extreme. That explains why there are, so often, fraught exchanges as couples pick their way towards workable relationships with mothers- and fathers-in-law, and as live-together lovers cope with the often suspicious parents of their partners.

None of this is easy, but it is the way successful families forge a way through life. In the case of my acquaintance, things are going well. When it came to the inevitable rows about how they conducted their lives, husband and wife stood together until peace was declared. They appear to be heading for a workable modern life, something many other families - the Windsors included - seem to be unable to achieve.