I have just never understood why on earth anyone should think that it's important or in any way beneficial for royals to spend time together. The UK and Sweden, Netherlands, Norway etc. are allies and have been for a long time. Those diplomatic relationships don't really need improving or developing as they're already strong.
The BRF clearly prefer to socialise with their own friends, as opposed to foreign royals. I fail to see what's wrong with that. Members of other royal families get invited to the big British royal events, and the Queen always sends one of her children to their royal events.
Victoria and Daniel were invited to William's wedding because it's what was expected. Had W & K had the option of inviting only those whom they're close to, it's very unlikely that they would've been there. It's hardly surprising that William doesn't recognise all the 2,000 guests that attended his wedding.
I'm not talking about diplomatic relations between countries.
In that respect the royals is a diplomatic tool for the politicians.
I'm talking about fostering a bond between people in a similar situation. Exchanging views and ideas, thinking outside the traditional box, learning from the experiences of others from the horse's mouth, rather than through the press or through councellors.
Chatting about something as crucial as how to prepare your children for their future role.
Royal spouses will find such exchanges extra beneficial, especially as the public can be very unforgiving if they make mistakes.
With all due respect for the BRF, there are not that many other royal families in Britain.
Who can say Kate go to if she has problems, ideas or would like to be inspired? Her husband? Only so far, as he was born into his role.
QEII? She is much older. Camilla? She's a generation older and what if they don't have a good rapport?
There are not that many.
Daniel on the other hand, has at least three other royal spouses in the exact same position as him, whom he can look to, ask for advise or went his frustrations with.
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Going back on track. Here are two HQ pics of Kate, William and Duchess Camilla:
http://www.bt.dk/sites/default/files-dk/node-images/416/5/5416462-oly-eque-eqxi3deqx003301.jpg
http://www.bt.dk/sites/default/files-dk/node-images/416/5/5416413-william-og-kate-4.jpg