The Duchess of Cambridge took on a more junior role with Prince Edward the official host of the event as the most senior person in the line of succession. With Prince William away, Kate took a backseat to the Earl and Countess of Wessex.
The monarch’s cousin Princess Alexandra also attended the garden party.
It comes after the Palace announced that the Queen will miss the royal garden party season and be represented by other members of her family.
Kate wore a pink dress by Emilia Wickstead for the garden party on Wednesday.
The Duchess completed her outfit with a clutch bag, hat and pair of heels in similar shades of pink.
The 40-year-old smiled as she mingled and chatted with guests during the event.
Meanwhile, Sophie was elegant in a cream gown with a red, blue and black floral pattern.
Garden parties are being staged for the first time in three years following the Covid pandemic.
The Palace announced earlier this month that the Queen would not attend the events this year.
Buckingham Palace said: “Her Majesty The Queen will be represented by other members of the Royal Family at this year’s garden parties, with details on attendance to be confirmed in due course.”
The 96-year-old monarch, who attended a surprise royal engagement yesterday, has been suffering from ongoing mobility issues.
It is understood the key factor in other royals being asked to represent the Queen was the length of time hosts spend standing during garden parties which last well over an hour.
They are important events in the royal calendar as those who have served their country or communities are recognised.
The Queen traditionally hosts three garden parties a year at Buckingham Palace and one at Holyroodhouse.
Royal author Angela Levin told the Daily Mail: “It’s a good decision for the Queen not to attend garden parties as there would be too much standing. What a shame though.”
This year’s garden party season was kicked off a week ago by Prince Charles and Camilla.
As the rain poured down, the Prince of Wales and the Duchess of Cornwall spoke to a selection of the 8,000 guests in attendance.
It comes as the Queen has missed a number of major events this year but has been carrying out virtual engagements and her other duties.
She made a surprise appearance on Tuesday to officially open the completed Elizabeth line, named in her honour.
The head of state, who now rarely carries out public engagements outside of her royal residences, joined her Edward at Paddington Station.
The Queen, who was radiant in yellow, met staff who have been key to the project and who will run the railway, including train drivers, station staff and apprentices.
A Buckingham Palace spokeswoman said: “In a happy development, Her Majesty The Queen is attending today’s event to mark the completion of the Elizabeth line.
“Her Majesty was aware of the engagement and the organisers were informed of the possibility she may attend.”