As rumours swirl around Meghan Markle and Kate Middleton's relationship, an expert advises on how to get on with your sister-in-law, when you're thrown together by circumstance.

They face daily scrutiny for their wardrobes, hair and charity choices. But now the Duchess of Cambridge and Duchess of Sussex’s relationship is under the microscope, with claims their bond is far from perfect.

The Duke and Duchess of Cambridge and the Duke and Duchess of Sussex at Westminster Abbey on Armistice Day.
The two royal couples together at Westminster Abbey (Paul Grover/PA)

But whatever the reality of Kate and Meghan’s friendship status, the question we’re asking ourselves is this: Why should they necessarily be besties?

Like sisters-in-law the world over, they are linked through family ties: The two wives of two brothers, with different backgrounds and upbringings. This is not a friendship you choose for yourself.

But, with the right attitude, it can be a happy tie. Here’s how.

Keep expectations low
This is a woman you wouldn’t necessarily have chosen as a friend and suddenly you’re expected to be bosom buddies. Hilda Burke, psychotherapist and couples’ counsellor, says: "If the expectations are really high, that can be counter-productive. I think we’ve all had experience of a sister-in-law or someone trying to be our friend, which can be a real turn off. So, rather than faking interest, see if you can just be yourself and see what comes of that."

Prince Harry, Meghan Markle and Kate Middleton arrive at the wedding of Princess Eugenie (PA)
Family events such as a wedding are times when you’ll be in the same place as your sister-in-law (PA)

Be patient and give it time
"It’s like an arranged marriage," says Burke. "You’re committed for life. Some brothers don’t speak, and some people don’t know their sister-in-law, but for most of us it’s ‘this person is going to be around… forever’.  It takes time to get to know her and see how it will be. At the start, it can be quite daunting – especially if the brothers are close and get on."

The Royal Wedding
Pippa carries Kate’s train as she arrives at Westminster Abbey (PA)

Think about your ‘sister legacy’
Someone with a close sister, like Kate, might not ‘need’ a new ‘sister’ – but now she has one and they’re both bringing family history to the dynamic. For Meghan, there’s a half-sister who has been vocal about Meghan’s new life. Suddenly Meghan and Kate are ‘sisters’ too.

People who have maybe had a sister or half-sister they’ve been pitted against growing up might be more likely to be wary of a sister-in-law, says Burke. "We can set ourselves up to be wary of them and feel that we’re going to be judged against them. If you’ve had that experience, you might need to be mindful of not provoking your sister-in-law."

Check in with your partner
As with a mother-in-law, it could be your new husband doesn’t want you to be best mates with his sibling’s wife. Plus, your sister-in-law will already know your husband – possibly for longer than you have.

It’s a case of exploring this with your partner and the other woman, and considering what you want that relationship to be, says Burke. "Your husband might not want you to be best friends," she warns. "Ask, how can we make it cordial?  It’s important to have that conversation with your partner as well.

"Sometimes women can falsely believe that their husband wants them to be best friends with their sister-in-law. The husband might just want there to be a bit of peace and calm between them."

The Duchess of Cambridge and The Duchess of Sussex in the royal box on centre court on day twelve of the Wimbledon Championships at the All England Lawn Tennis and Croquet Club, Wimbledon.
Kate and Meghan spent the day at Wimbledon this summer (PA)

Find common ground, but don’t force it
It’s rare to see the duchesses out together. They keep their engagements separate – and that’s fine. After all, not many of us go to work with our sister-in-law. You don’t have to live in each other’s pockets and suddenly try to do all the same things as her. If she’s into classical and you’re more Little Mix, don’t be booking the Albert Hall just to try and please her.

"If you force it too much, the other person will sense that and feel it’s out of duty. If we do things out of duty they tend to fail, or we tend not to stick to them," warns Burke.

And if you don’t get on…
"Think about what’s provoking it," advises Burke. "Maybe it’s envy or jealousy, in which case that’s something you need to work on. Has she got a bigger house, more kids… perhaps she doesn’t have kids and she still has her freedom?

"Sometimes, what can be stirred up in these relationships is our own stuff! Rather than trying to cover it up, deal with your own stuff that you’re bringing to this relationship. It might be that once you put down your animosity then you might naturally want to spend more time with her."