However, the pair seem to get along well. They have been spotted chatting and laughing at royal events such as Trooping the Colour.
While different in age and background, it appears they have an affinity.
Both represent a different era in the Royal Family.
Prince Philip, a veteran who served in the First World War may not have appeared to have much in common with Kate, who was born into a middle class family to an air hostess and business man.
Judi went on: “Kate must have passed muster with the prince in terms of proving herself as a trouble-free and loyal royal bride.”
There is a shared humour between the two, much like Kate’s relationship with Harry.
Judi said: “There seems to be a natural proximity between the two and Philip does seem to have stepped into Harry’s shoes in terms of being the royal who can make Kate laugh at more formal events.”
But, this doesn’t mean it’s an opportunity for Kate to let her hair down.
The expert added: “Kate’s body language suggests she is on her best behaviour with Philip, as she does with the Queen, but this appearance of respect lends a very real ‘in-laws’ look to their body language rituals.”
In recent times Kate has been undertaking more solo visits without her husband Prince William.
Kate Middleton visited Derby University this week to learn about student mental health.
Judi analysed this trip to, telling Express.co.uk the Duchess demonstrated she has the “power and influence to help create change”.
Judi said: “Dressed in smart, chic but un-fussy casuals, Kate strode into the university like a woman on a mission, oozing confidence with her bag-free hands hanging by her sides.
“Her arrival reflected her tone of concern for the mental health of the students there and throughout her visit that overall tone looked enquiring as well as encouraging and uplifting.”
For the visit Kate Middleton wore a £249 coat and a necklace with a message to her children.