Mum-to-be Zara was joined by her own mother, Princess Anne, for their day at the Fesitval of British Eventing.
Zara's appearance at Gatcombe comes as a surprise to some as it contradicts a statement from her representitives which said that the young royal would not partake in any horseriding during her pregnancy.
A spokesperson for the Queen's grand-daughter said that Zara's pregnancy – it is thought that she is in her third month with her first child with husband Mike Tindall – is progressing "happily and healthily".
The representative confirmed that the royal is being "sensible" and said that Zara had cancelled all trials until after the birth early next year.
"She has done so well already this season, she does not actually need to compete any more. Given that she is pregnant, she has decided to cancel the rest of her entries for the year."
The keen equestrian fan displayed her first maternity outfit at Ladies' Day at Glorious Goodwood on Thursday.