Buckingham Palace and William and Kate shared photos of Camilla on Twitter on Sunday alongside birthday messages and cake emojis.
The Queen’s @RoyalFamily Twitter account tweeted: The Duchess from Cornwall a very happy 75th birthday!”
Additionally, Buckingham Palace shared a photo of Camilla beaming while holding her Jack Russell terrier, Beth.
Getty Images royal photographer Chris Jackson, who took the photo, retweeted the post, adding: “A very happy birthday to HRH The Duchess of Cornwall, 75 today!
“Pictured on the steps of her shepherd’s hut at home in Wiltshire with lovely Beth.”
The Cambridges’ @KensingtonRoyal account also sent greetings to Camilla, tweeting: “Wishing the Duchess of Cornwall a very happy 75th birthday today!”
An accompanying photo, taken by Kate, shows Camilla, dressed in a cardigan and floral dress, walking through a meadow of forget-me-nots.
The Prince of Wales and Camilla’s @ClarenceHouse account confirmed the messages, saying: “Thank you for all your kind messages and well wishes on the 75th anniversary of The Duchess of Cornwall today!”
It comes after an official photo of the future Queen Consort was released on Saturday to mark her birthday.
It shows Camilla sitting at a garden table with flowers and plants in the background and a teacup and saucer in front of her, along with a bowl of peaches.
The photo was taken last month in the gardens of Raymill, Camilla’s retreat in Lacock, Wiltshire, where the peaches photographed were grown.
She bought the six-bedroom property, 17 miles from Charles’ home in Highgrove, after her divorce from Andrew Parker Bowles in the mid-1990s.
The Duchess is wearing a blue Sophie Dundas floral dress in the photo taken by Getty Images.
Clarence House said her birthday would be celebrated with a small family dinner on Sunday.
It is likely that Charles will host the evening gathering and guests will likely dine at Highgrove.
Camilla’s daughter, Laura Lopes, and son, Tom Parker Bowles, are expected, along with her younger sister, Annabel Elliot.