Sister-in-law Autumn Phillips could hardly contain her mirth – head thrown back and eyes closed as she laughed away.
Around her, Peter Philips, Princess Beatrice and Zara's husband Mike Tindall also had a good giggle as the group checked out the equestrian action at Royal Ascot.
The group was joined by Zara's pal Tina Cook – who rode with her in Team GB's team at the London Olympics.
Zara was at one point spotted giving her husband a kiss on the cheek - but it looked as if someone else had beaten her to it.
It appeared as if rugby player Mike had dark-coloured lipstick marks on his face, but in fact they were due to an accident he sustained while playing for his team, Gloucester, on Thursday.
Mike was forced to leave the pitch 52 minutes into the game against Bordeaux with an injury. And the marks looked as though they were the result of another player's studs being dragged across his face during a rough tackle.
The young royals were joined by the Queen – elegant in a white textured jacket and matching hat and diamond brooch – who looked thrilled to be watching her favourite sport with her family by her side.