While Kate seems to have a good relationship with all of her in-laws, she is particularly close to Prince Philip, body language expert Judi James explained.
Prince Philip may have retired from royal duties in August 2017 but he has stepped out with Kate on occasions before this.
Analysing pictures from Trooping the Colours in 2017, Judi explained Kate is a hit with her grandfather-in-law.
Judi told Express.co.uk: “These delightful poses suggest unexpectedly rich bonds between Kate and Prince Philip based on not just affection but also a shared sense of humour and fun.”
Both Kate and Prince Philip have shown they have a shared sense of humour.
Trooping the Colours is a serious event but the Duchess and Prince Philip still managed to share a joke.
Judi added: “Both royals tend to be fans of protocol at public events but Philip’s animated chat here puts could have put them firmly on the naughty step, as judging from the poses of the rest of the group they are having a chat and a giggle during a fly-past.”
While Kate was relaxed, Prince William seemed more cautious about getting involved in the joke.
“William previously got a telling off from his gran for bending with his son during a similar line-up,” Judi explained.
“There’s a hint of wariness about his smile and self-protective fig-leaf hand positioning here that suggests he’s not keen to repeat the experience by joining in the fun too wholeheartedly.”
Kate was happy to give her attention to Prince Philip while still making sure her younger children were alright.
Judi said: “Kate manages to control her two boisterous children with her hands while turning her head to pay full eye-attention to Philip.
“Her dimpled smile and softened eye expression show genuine affection but her fully opened-mouth laugh suggests she’s finding Philip’s comments genuinely hilarious.”
Since joining the Royal Family, Kate has become a popular royal in her own right.
As well as being a hit with the public, Kate seems to have a good relationship with other royals.