NATASHA LIVINGSTONE: Outspoken Anne has had her differences with Charles. But today she is his “right hand” – the sister who truly understands the pressure he now faces. They are bound together by circumstances and duties…

She was the star of the documentary King's Second Day with her candid commentary, sharp insight and tendency to make her brother – and undoubtedly the viewers – laugh.

Who else would greet the new Charles with “Hello, Old Bean”?

It was Princess Anne who explained to BBC viewers how difficult it had been for her brother to prepare for the coronation, despite a lifetime of waiting in the wings.

And it was Anne who summed up Charles's feelings after the ceremony as those of “an actor coming off stage after a performance they've really put a lot into.” It's that kind of relief.”

The Princess Royal is increasingly described as the 'right hand of the King' and is emerging as a figure of shared understanding and trust.

Anne, Princess Royal pictured wearing a two-horn hat with towering feathers during the coronation of King Charles III

Princess Anne tells Household Division officers that the monarchy is safe in Charles' hands

Next week she will fly to Sri Lanka for the first royal tour of 2024. The three-day trip, made at the request of the Foreign Office, marks 75 years of diplomatic relations with the United Kingdom.

However, such close cooperation has not always been so self-evident.

For much of their adult lives, Charles, now 75, and sister Anne, 73, led rather separate lives and there was a time when relationships were thought to be decidedly cool.

Their respective country houses, Highgrove House and Gatcombe Park, may have been only six miles apart in the Cotswolds, but there was little evidence of family visits.

They obviously have different interests and approaches, as their very different homes might suggest.

The manicured Highgrove with its lovingly maintained gardens is a living work of art.

Princess Anne's Gatcombe is an impressive shrine to all things equine: part stables, part family compound, with children, grandchildren and even exes living on site.

Anne was born less than two years apart and was always more outgoing than Charles.

She was considered close to Prince Philip and was known for her brusque, non-nonsense demeanor. She was once described as 'very much her father's daughter – in a way that Charles could never be his father's son.'

They also have a number of things in common, not least a sense of humor (Charles is surprisingly funny) and a commitment to sheer hard work.

Analyzes of last year's royal engagements disagree on who was the hardest-working HRH, but on this they agree: it was either the King or the Princess.

Anne completed 457 assignments, while Charles completed 425, according to The Daily Telegraph.

The Times says Charles carried out 516 engagements at home and abroad, with the Princess Royal completing 410.

There is little time for home visits.

Despite all their differences, Charles and Anne are bound together by circumstance and duty – a bond that is as evident now as ever before.

King Charles III and Anne, Princess Royal attend the Committal Service for Queen Elizabeth II at St George's Chapel, Windsor

Anne, Princess Royal, publisher Sir Nicholas Coleridge (c) and King Charles III at last year's Braemar Games

Prince Charles, Prince of Wales, Queen Elizabeth II and Princess Anne, Princes Royal attend the 2018 Braemar Highland Gathering

The Princess Royal and Prince Charles, Prince of Wales attend the funeral of Patricia Knatchbull, daughter of Louis Mountbatten at St Paul's Knightsbridge in 2017

Prince Charles, Prince of Wales and Princess Anne, Princess Royal at the Platinum Pageant on The Mall in 2022

Four generations of the British monarchy pictured together at Buckingham Palace after Princess Anne's baptism in 1950. From left to right: Queen Mary, King George VI, Queen Elizabeth II, Prince Philip, Prince Charles and Queen Elizabeth, the Queen Mother

Princess Anne was known as a 'daddy's girl', seen here with her hand over Prince Philip's mouth

Princess Anne was not present at the coronation, although Prince Charles was taken halfway through. But the two-year-old then came out onto the balcony and stood next to her big brother

Prince Charles (6) and Princess Anne (4) pose with their mother in 1954

Duke of Edinburgh, Princess Anne, Prince Charles and Queen Elizabeth II, pictured looking down from the east terrace wall of Windsor Castle in 1959

Princess Anne, Prince Charles, Tony Snowdon and his new sister-in-law Queen Elizabeth II watch the Badminton Horse Trials in 1960

Princess Anne, Prince Charles, Prince Philip, Duke of Edinburgh and Queen Elizabeth II meet Richard Nixon, President of the United States in February 1969

Prince Charles side by side with sister Princess Anne in February 1970

Of the late queen's four children, only two knew their mother before life changed with her accession to the throne.

Accidentally or otherwise, it was Charles and Anne who were at Elizabeth's side during her final moments at Balmoral, not the young people.

A lifetime earlier, when she was a blond-haired two-year-old, Anne had been left behind in the palace when Charles, the future king, was taken to attend their mother's coronation.

But she will know everything there is to know about what her big brother went through in those extraordinary seventy years of waiting to play his role – and what he now faces in the time remaining.