They have known each other less than 24 hours. But by the looks of their warm greeting, the Duke and Duchess of Cambridge and their Swedish Royal counterparts are firm friends already.
The two Royal couples embraced one another like old friends, with double kisses on the cheek all round and a few stolen moments to catch up privately before they began their first engagement.
When the Duke and Duchess of Cambridge embarked on a tour to Scandinavia, a spokesman said they planned to build relationships with Royals of the same generation abroad.
Although they are similar in age, ranging from 35 to 44, the couples have rather different status: Crown Princess Victoria is first in line to the Swedish throne, following her father King Carl XVI Gustaf.
Prince William, who is second in line of the throne after the Queen and the Prince of Wales, is in fact closer in rank to Victoria’s daughter Princess Estelle, aged five.
In the afternoon, the Duke and Duchess joined Princess Estelle and Prince Oscar for tea, as the children settled in next to their parents on a comfortable sofa at their home of Haga Palace.
Tucking into snacks, the second-in-line to the throne and her little brother listened to the grown-ups talk as the families got to know one each other better in their final hours of the Royal visit to Sweden.
The two Swedish children will have given the party plenty to talk about, as they are close in age to Prince George and Princess Charlotte.
On their second day in Sweden, the Duke, Duchess, Princess and Prince also undertook two events focusing on mental health, and a visit to department store NK to open an interactive exhibition of UK design, fashion and brands.
At the Karolinska Institute, they were given a briefing with senior staff including Professor Carl Johan Sundberg, Dr Anna Lundh and Dr Ulrika Berg about their research into mental health.
"We have a problem with the growth of mental health disorders here in Sweden," said Dr Lundh.
"We are trying to create a programme where we standardise treatment packages and place as much emphasis on physical activity, looking at sleep, looking at eating behaviour, as we do on psychology and pharmaceuticals."
Dr Berg said: "I am a paediatrician and meet a lot of children with mental problems. It is absolutely important that we use physical activity as a tool for prevention and also for treatment for…mental diseases such as depression.
"I think people think ‘oh, it is good for children to move’. But it has really been shown, in research, that there are important effects, for example in depression when we know that self-esteem increases, we know that regular physical activity of an aerobic kind, three times a week and adding skeleton load and muscle strengthening activities will lead to many positive health benefits. And it doesn’t have any side effects."
The Duke asked: "The increased number of mental health issues coming forward, are they increased or are they more seen because of conversations or because of mental health becoming a little less stigmatised?"
He was told that there was a real increase in people diagnosed with depression and anxiety in Sweden. Why are the [number of] girls higher than boys?" he continued.
"We do not know,’ he was told, as academics confirmed that there was definitely an increase in anxiety in young girls.
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"And now those girls are becoming mothers themselves," interjected the Duchess.
After the briefing session, they moved to Matteusskolan School to learn more about a programme to encourage children to speak about their feelings.
They were greeted by a line of pupils, offering handshakes, high fives and fist bumps to children of all ages.
Malte Bregqvist, 15, said: "I shook both their hands. It was weird, I never really met a royal before. I asked them how they were and they said the same thing to everyone, they were nice, they were doing fine.
"It’s generous of them to take time and shake everybody’s hands. They are supposed to be talking about kids physical and mental health – it’s about a programme running here."
One cheeky pupils asked the Duchess whether she was familiar with the work of J Hus, a rapper.
"I will look out for him," she promised.
Kate and William’s tour of Sweden and Norway
In a speech to students, the Duke said: "Catherine and I and Victoria and Daniel care deeply about mental health.
“It’s all about early intervention. Sometimes a conversation is enough.”