The Duke and Duchess of Cambridge attended the Royal Variety Performance on Thursday evening, with Kate wearing a beautiful long green Jenny Packham gown and her husband donning a smart tuxedo.
MORE: Kate Middleton's hearty family diet at home with Prince William and their children
While the royal couple were photographed on their way into the venue, however, their special guests were only spotted by an eagle-eyed attendee, who shared their observation to Twitter.
Seated to the left of the Duchess were her parents, Carole and Michael Middleton, as well as her brother James and his new wife, Alizée Thevenet, who he married back in September in an intimate ceremony in France.
WATCH: William and Kate attend Royal Variety Performance
The Middletons are very close to Kate and it was a sweet gesture for them to be included in the festivities in what was the royal couple's fourth appearance at the special event.
SEE: Carole Middleton's new Christmas decorations have George, Charlotte and Louis written all over them
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Held at London's Royal Albert Hall on Thursday, Prince William and Kate walked the red carpet before taking their seats in the royal box.
The crowd sang the royal anthem before taking their seats
The event is in aid of the Royal Variety Charity, of which the Queen is patron.
Money raised from the show helps hundreds of entertainers throughout the UK, who need help and assistance as a result of old age, ill-health, or hard times.
This year sees the centenary of the reigning monarch being patron, commencing with King George V in 1921.
The royal couple looked so stylish
While the Queen did not attend the event, she had a surprise guest of her own during her latest public event – and it made for an adorable interaction!
On Wednesday, the 95-year-old monarch met face-to-face with General Sir Nick Carter, the Chief of the Defence Staff, at Windsor Castle.
In footage released by Buckingham Palace, the Queen's inquisitive dorgi Candy could be seen greeting General Sir Nick in Windsor's Oak Room. After bowing to Her Majesty, he chuckled and said to the royal pooch: "Hello you."
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