Lindy McDowell: Sisters-in-law don't have to be best mates but they can support each other
You know the old saying? You can choose your friends but you can't choose your family? In the case of in-laws it's more complex still.
Somebody else in the family gets to choose them.
To put it another way, they become part of your own extended family by dint of marriage.
Given the chances then, why should in-laws ever get on?
The odd thing is that generally they do. I know this from my own experience.
I've had four sisters-in-law - two of whom, the best, funniest, loveliest most open-hearted women you'd ever have hoped to meet, died far, far too young.
It would be a lie to say my sisters-in-law and I were as close as sisters (although I know that in some families that is the case.)
It's a slightly different relationship.
And yes, you can see why in the case of Kate, Duchess of Cambridge and newcomer Meghan, Duchess of Sussex, it could also be a competitive one.
Two beautiful young women (one an actress with a fondness for the spotlight) now both vying for centre-stage?
What could possibly go wrong there?
One has a television career behind her, the other has the weight of history. One is Hollywood royalty. The other will be Queen.
How much truth there is in recent reports of a fractious relationship between the pair we can't know for certain. But on the "no smoke without fire" scale it does seem there is some sort of clash. Meghan is portrayed as overbearing, bossy, demanding. She's said to have left Kate in tears during a bridesmaid dress-fitting for little Charlotte. Other charges are that she gets up at 5am to send emails and she wanted to fumigate Windsor Castle. Or at least spray St George's Chapel with air freshener prior to her wedding.
What Meghan wants, Meghan gets, Prince Harry is reported to have said. Words that will surely haunt them both.
Teary-eyed Kate would seem to have emerged from all this the victim. But since she's also being described by royal insiders as a "steel marshmallow" (the description was first used about the Queen Mother during the abdication saga) she may not be quite the pushover this makes her appear.
Maybe she gave as good as she got?
And what of the brothers, William and Harry? We've always known they were close, not just because royal "sources" told us but because we could see it in pictures and footage of the pair. Their bond was obvious.
Even when Kate came along...
Meghan has changed the dynamic - but maybe that's just inevitable. Even a bit overstated.
Much has been written about Harry and Meghan's proposed house-move away from Kensington to Frogmore which is all of about 25 minutes down the road.
The way some commentators have reacted you'd think the pair of them were heading for Outer Mongolia.
The unusual thing here isn't that Harry and his new wife have decided to relocate. It's that in his mid-30s he's still been living next door to his brother.
Not all extended families live in a family "compound." And I think we're all the better for it.
But Meghan moving a bit out of Kensington is unlikely to call a halt to what is being portrayed anyway, as the rivalry between her and Kate.
It is going to take more than just a few smiley group appearances - and an end to those damaging "leaks" from "insiders".
The tabloids and gossip mags are salivating at the thought of further ructions in the House of Windsor.
Two beautiful, titled young women supposedly at each other's throats? This is red-top manna from heaven.
Even Dear Deirdre has offered advice.
On television meanwhile, Piers Morgan, a man known to drop the odd name or several hundred, describes how he was 'ghosted' - let go as a friend by Meghan as soon as she met Harry. The inference being that Piers was no longer of use to her...
I do feel sorry for Meghan. She's pregnant and she's far from home with only her mother and Harry for support.
She doesn't seem to have a whole lot of friends. Her own dysfunctional family famously did her no favours in the run-up to her big day.
But maybe if she'd tried to get along a bit better with them...?
Kate, meanwhile, as the longer-established member of the royal firm should perhaps dry her eyes and offer a bit more guidance. Even if it's thrown back in her face.
Sisters-in-law don't have to be best mates. But as Diana and Fergie showed, they can get along and give each other real support.
Meanwhile, what of the two men at the centre of this rift? What have they been doing to smooth things over?
The problem for William and Harry is that as with any other family spat, once outsiders start chirping in - and stirring it - people understandably get their backs up even more.
Here, it's not just the neighbours gossiping about your nearest and dearest. Everybody's pitching in. It must be tricky.
But it's the poor old Queen I feel for most.
At her age, the last thing she needs is another annus horribilis - another animus horribilis.