Zara Tindall is the daughter of Princess Anne, 70, and Mark Phillips, 72. While she is the eldest granddaughter of the Queen, she is not a working royal.
When they are seen together, body language expert Judi James commented on their relationship.
Analysing pictures for Express.co.uk, she suggested they may have a different bond to other royals.
Judi said: “This looks like such a joyful and even indulgent relationship between the Queen and her grandchild Zara.
“It is perhaps made more relaxed because Zara is not an official member of ‘The Firm’ and so can see and treat the Queen purely as her grandmother, rather than also being her boss.”
As well as having a close relationship, she said they have some key similarities.
In one snap taken at the Royal Ascot, Zara is seen crouching down next to the Queen.
Both women can be seen pointing at something in the distance.
By mirroring each other’s body language, Judi suggested they have shared “empathy”.
This could be something that the Queen enjoys, the expert added.
“There are three key body language signals defining the strong bonds of affection here, their proximity, their touch rituals and their mirroring,” Judi continued.
“Zara is probably the most openly tactile and spontaneous-looking member of the Royal Family as well as being the most good-humoured-looking one.
“Both those qualities seem to have a very positive effect on the Queen, allowing her to be more openly demonstrative than she is seen to be in public with most of her other relatives.”