Anne was rushed to hospital two months ago after suffering concussion and head injuries in an accident involving a horse while walking on her Gatcombe estate.
The princess underwent a phased return to public duties, but has forged ahead with her official engagements over the summer, travelling to Paris for the Olympics and, last week, attending the Royal Edinburgh Military Tattoo.
The monarchy’s official social media accounts shared archive images of the princess, alongside the message: “Wishing The Princess Royal a very Happy Birthday today!”
Among the pictures was a black and white photograph of a three-year-old Anne with her older brother Prince Charles, then five and now the King, sat among the daffodils at Royal Lodge, Windsor, in 1954.
The Royal Collection Trust posted a throwback portrait of the princess as a 21-year-old.
It shows a glamorous Anne, with her hair half up half down in bouffant style, dressed in a floor length floral voile gown with long sleeves as she leans against a stone arch in the gardens of Frogmore House, among the vegetation.
The black and white image was taken by celebrated fashion photographer Norman Parkinson in August 1971.
Dubbed the King’s right-hand woman in the wake of Charles’s cancer diagnosis, Anne is often seen as the hardest working royal and known for her dedication to duty and no-nonsense approach.
Princess Anne Elizabeth Alice Louise, the only daughter of the late Queen Elizabeth II and Prince Philip, the Duke of Edinburgh, was born at Clarence House on August 15 1950.
She is the mother of silver medal-winning Olympic horsewoman Zara Tindall and businessman Peter Phillips.
Anne is involved with more than 300 charities, organisations and military regiments.
She competed in the 1976 Montreal Olympics as a three-day eventer in the British equestrian team, and is now president of the British Olympic Association.