But when they do, we get an insight into their close bond and sweet relationship.
And that was proved last week when Kate and Charles attended the world premiere of the new James Bond movie with Prince William and the Duchess of Cornwall at the Royal Albert Hall.
Cameras snapped the pair affectionately greeting each other with a kiss on the cheek, with experts saying it shows their “rather tight relationship”.
Here we look back at how they developed their bond and now enjoy being in each other’s company…
Kate and William started dating while they were students at St Andrews University in Scotland.
And it appears even in those early days and before the pair announced their engagement in 2010, Charles welcomed his would-be daughter-in-law into the family with open arms.
In an interview to mark their engagement, Kate said Charles had been “very, very welcoming” and “very friendly”.
She admitted that she was nervous to meet her future father-in-law but added: “It couldn’t have gone easier, really for me.”
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Months after their engagement was announced, Kate and William wed in a grand ceremony in Westminster Abbey in April 2011.
Proud dad Charles was there to watch his eldest son tie the knot and gave a tear-jerking off-the-cuff speech about the couple during a champagne reception at Buckingham Palace.
And according to Hello! he described Kate as like the daughter he never had and said: “We are lucky to have her.”
He then wished the couple a lifetime of happiness together.
POOL/AFP via Getty Images)
Although joint public appearances between Kate and Charles have been few and far between, when they have happened, the pair are often spotted sharing private jokes.
Last year in a visit to a veterans rehabilitation centre in Loughborough, Kate was pictured in fits of giggles as she stood next to her father-in-law.
William and Camilla were also there on the visit, and body language expert Judi James told the Express that by wrinkling her nose, Kate’s laugh shows “genuine humour and rapport”.
She added: “The affection Kate clearly feels for her father-in-law could be one big thing she has in common with Camilla.”
Healing rift between Charles and William
Despite Kate and Charles’s sweet relationship, the bond between Charles and William is said to have been rocky in the past.
But according to reports, it was Kate herself who helped to smooth things over between her husband and father-in-law.
And she did this by reportedly helping to organised a family portrait for Charles for his 70th birthday in 2018.
According to the Daily Mail, Kate was instrumental in making the portrait happen, which sees Prince George and Princess Charlotte beaming and cosying up to both Charles and his wife Camilla.
While the Duchess herself snapped a lovely symbolic photo of Charles and his eldest son on William’s birthday in 2018, in which Charles can be seen resting his head on her husband’s shoulder.
Organising grandparent time
Charles is now the proud grandfather of five grandchildren, including Kate and William’s kids Prince George, Princess Charlotte and Prince Louis.
But previously there had been claims that Charles, 72, was unhappy he did not get to see enough of the trio.
In an interview two years ago to mark Charles 70th birthday, Prince William echoed the sentiment.
He said: “I would like him to have more time with the children… to, you know, play around with the grandchildren.
“When he’s there, he’s brilliant, but we need him there as much as possible.”
To this end, Kate is said to have urged Charles to visit their home Amner Hall last summer and took on the logistical challenge of getting her family back home from a holiday on the Isles of Scilly to coincide with his visit.
In doing so, it was reported that the heir to the throne was able to give his grandson George a seventh birthday present in person.
Comfort at funeral
Earlier this year, the royal family were left grief-stricken when Prince Philip died aged 99 at Windsor Castle.
at his father’s funeral as he led the procession to St George’s Chapel.
After the ceremony, Kate was spotted comforting Charles by putting her hand on his shoulder and giving him a kiss on the cheek.
He goes by the names of His Royal Highness, the Prince of Wales and Charles – but Kate appears to have an endearing nickname for her father-in-law – showing their happy relationship.
Kate, Charles, William, Camilla and the Queen were all at a drinks reception at the G7 summit in Cornwall in June.
And it seemed as though Kate referred to Charles as “grandpa” as they arrived at the reception at the Eden Project.
A lip reader told CornwallLive that the Duchess of Cambridge had used the moniker for her father-in-law.