Barbara died peacefully on July 2 at Horsfall House in Minchinhampton, according to an obituary shared in the Telegraph.
The 90-year-old was the "much beloved widow of Guy," and mother to sons Jonathan and Tim.
Barbara's funeral will be held at St Giles Church in Great Wishford on July 20 with a wake to follow at The Royal Oak pub.
Widely regarded as the hardest working member of the British royal family, Princess Anne has enjoyed a long running and colourful career as the only daughter of Her Majesty Queen Elizabeth II and Prince Philip, Duke of Edinburgh.
The famously feisty Princess Royal has been married twice, first to Captain Mark Phillips - with whom she shares son Peter and daughter Zara - and then to Timothy.
The couple have been together ever since and while they keep their private life largely out of the spotlight, they’re often spotted together at public events and royal engagements.