The 15-year-old dressed for the cooler weather in a navyblazerand trousers and a floral patterned blouse as she walked throughBurghley HouseinStamford.
On the other hand,Sophie, Countess of Wessexwore a red and pink striped skirt and a black T-shirt and could be seen laughing with her daughter from the grandstand at the event.
Later, the 54-year-old was presented with a bouquet of flowers and was seen chatting with sports presenter Clare Balding.
Sophie- who is married toPrince Edward,theEarl of Wessex- and Louise were visitingLincolnshirefor theLand Rover Burghley Horse Trials, an internationally recognisedequestrianand social event.
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Lady Louise is the eldest child of Prince Edward and is Queen Elizabeth II's youngest granddaughter (making her twelfth in line to the throne).
The Wessex family is more private than the other British royal families and they attend very few public engagements compared to Prince William and Kate Middleton.
According to the Daily Mail,this is the third time that the children of Prince Edward and the Countess of Wessex have made public appearances recently.
In July, the Earl and Countess of Wessex were spotted with Louise Mountbatten and her brother James Viscount Severn (the youngest grandchild of Queen Elizabeth II and Prince Philip) at a zoo in Bristol.
In June, the family attended the Trooping the Colour event along with the rest of the royal family for the Queen's birthday.
In a rare public appearance, Lady Louise Windsor was spotted at the Burghley Horse Trials with her mother Sophie Wessex on Sunday.
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Sophie and Edward celebrated their 20th anniversary in June.
"Edward became what one friend described as ‘unnerved’ by the speed which the affair was developing," Ingrid wrote of their relationship in her 1995 bookPrince Edward.
However, everything was back on track by the Christmas of 1994, and the couple went on to have their royal wedding at St George’s Chapel in June 1999.
James, Viscount Severn, Prince Edward, Earl of Wessex, Lady Louise Windsor and Sophie, Countess of Wessex visit The Wild Place Project at Bristol Zoo on July 23, 2019 in Bristol, England.