The Kensington Royal Twitter account shared a sweet birthday message to Camilla, alongside a photograph of her at an event raising funds for a conservation charity founded by Camilla’s late brother Mark Shand.
The caption read: “Wishing The Duchess of Cornwall a very happy birthday today!” followed by a balloon emoji.
The Royal Family’s official Twitter account also sent their own message to the Duchess of Cornwall.
They wrote: "Wishing The Duchess of Cornwall a very happy birthday today! #HappyBirthdayHRH".
Many others took to social media to share their well-wishes.
Westminister Abbey tweeted: “Wishing The Duchess of Cornwall a very Happy Birthday today!”
Former MP Gyles Brandreth wrote: “Happy birthday to HRH The Duchess of Cornwall - Countess of Chester and honorary graduate of â¦@uochester”.
Last year, Camilla celebrated her birthday with her family at Raymill, her private Wiltshire home.
The duchess had a busy week ahead of her 74th birthday, attending engagements in Yorkshire and London.
On Wednesday, Prince Charles and Camilla attended ‘A Starry Night In The Nilgiri Hills’ hosted by the Elephant Family at Lancaster House in London.
Speaking at the event, Camilla said: “In 2002, my beloved brother, Mark, helped create the charity Elephant Family, to protect Asia’s magnificent wildlife. Over the past few weeks, Londoners have had the rare opportunity to see some of that wildlife (albeit in static form!) on the Mall, in Green Park, in St James’s Park and in Berkeley Square.
“These magnificent, life-sized elephants have roamed – with a little help - from the Nilgiri Hills of Southern India, to the Cotswolds, to the heart of the city to raise awareness of the vital importance of healthy co-existence between humans and animals.
"They are a timely reminder to us all to live well with Nature, wherever we may be.”
The couple also attended the Great Yorkshire Show, where they met horse riders, farmers, and their livestock.