Princess Anne, the late Queen Elizabeth's only daughter and a former Olympic equestrian, turns 75 on Friday, with little fanfare planned in keeping with the royal's disdain for making a fuss.

To mark the occasion, Buckingham Palace is releasing a new photograph of the horse-loving princess, who is often credited with being the hardest-working member of the British royal family.

Born in 1950, two years after her brother, now King Charles, and two years before her mother would become monarch, Anne became renowned as a young princess for her rather brusque, plain-speaking public demeanour - reminiscent of her late father, Prince Philip.

But she went on to gain acclaim for her horse-riding triumphs, becoming Britain's first royal Olympian when she competed at the 1976 Montreal Olympic Games. More recently, she has been lauded for her campaigning for domestic and international charities.

A YouGov poll last week showed Anne was the third-most popular of the royals, just behind heir Prince William and his wife Kate, with 70% of those surveyed having a favourable view of her.

While other members of the Windsor family have become staple tabloid fodder, Anne has eschewed the limelight, although she was involved in one of the most dramatic royal events of modern times when an armed man attempted to kidnap her near Buckingham Palace in 1974.

She said her calmness in dealing with the incident - she told her would-be assailant "Not bloody likely!" when he demanded that she get out of her car - was due to her experience with horses that had helped make her prepared for the unexpected.

Last year, she spent five nights in hospital after suffering a concussion from an incident which involved a horse, but was back at work three weeks later.

"She just keeps her head down the whole time, keeps working away and leaves others to worry about column inches," her son, Peter Phillips, said in a TV interview last year.