When the Queen died earlier this month at the home she called her "paradise in the Highlands", two of her four children were by her side.
Her heir, Charles, rushed from his own Scottish home Dumfries House to join his sister, Anne, who was already by their mother's bedside.
"I was fortunate to share the last 24 hours of my dearest mother's life," Princess Anne said in a statement.
"It has been an honour and a privilege to accompany her on her final journeys."
Princess Anne was also chosen to accompany her mother's coffin on the long journey from Balmoral Castle to Edinburgh, and then on a flight to London.
As the Queen's only daughter, Anne has long held a special place in the House of Windsor.
She was extremely close to both her parents, an Olympian, and one of the hardest-working members of the family.
Last year, she carried out even more official engagements than her brother, making 387 public appearances to his 385.
Now 16th in line to the throne, Princess Anne has never been further from the crown.
Known for her no-nonsense attitude, unchanging hairstyle and work ethic, she has often flown under the radar during her siblings' scandals and dramas.
But as one of her brother's most trusted advisers, Anne's influence is set to grow.
There are even reports the new King wants to change an 85-year-old law so that his brother, Prince Andrew, his son, Prince Harry, and his niece, Princess Beatrice, will be removed from their positions as counsellors of state.
The shake up could see Anne promoted to a key position to fill in for Charles if he's unable to carry out official duties.
A headstrong princess called 'her royal rudeness'
Born 21 months after her brother Charles, the rules of the British monarchy always dictated that Anne would rank behind her male relatives in the line of succession.
When her mother ascended the throne in 1952, the then-18-month-old was second in line only to Charles.
But the arrival of her younger brothers, and eventually her nephews, sent her further down the ranks.
The law was eventually changed in 2015 so that new members of the royal family, like Princess Charlotte, would not be passed over for their male relatives.
The Queen gave Anne the title Princess Royal, an honour bestowed on the monarch's oldest daughter for three centuries.
But Anne's place in the House of Windsor never stopped her living her life the way she wanted.
An accomplished horse rider, she competed in the equestrian events for the 1976 Olympics.
"If it doesn't fart or eat hay, she isn't interested," her father Prince Philip once colourfully said of her love of horses.
As a teenager, the headstrong and outspoken princess was called "her royal rudeness" by the British tabloids.
"She has a reputation for having inherited her father's famously sharp tongue and waspish wit, once famously telling photographers to 'naff off' when they got in her way," royal writer Katie Nicholl wrote in 2020.
In 1974, an armed man ambushed Princess Anne's car in the Mall as she was driving with her then-husband Mark Philips.
According to declassified briefings of the incident, the man asked her to "come with me for a day or two" because he wanted a ransom of $3.4 million.
"Bloody likely!" she said to the gun-wielding, would-be kidnapper.
In a statement written for prime minister Harold Wilson, Anne said she was tempted to hit the man.
"It was all so infuriating; I kept saying I didn't want to get out of the car, and I was not going to get out of the car," she said.
"I nearly lost my temper with him, but I knew that if I did, I should hit him, and he would shoot me."
Locked in an argument with his intended victim, the man was eventually apprehended by police.
While Anne was often viewed as brash and haughty by outsiders, to her brother, she was a close friend and confidante.
The future king and his sister
With more than a decade between the births of Charles and Anne and their younger brothers Andrew and Edward, a strong lifelong bond was formed between the older siblings.
As a new Queen, their mother was often away on royal tours during their childhood years, leaving them in the care of staff.
"When his sister, Princess Anne, refused to leave their mother, he would drag her away, explaining: 'Anne, you must not bother Mummy. She's busy. She's queening'," royal biographer Kitty Kelley wrote.
As they grew older, they moved in the same social circles, and it's believed the siblings were at one point caught in a romantic entanglement with Andrew Parker Bowles and Camilla Shand.
Anne quietly dated Parker Bowles in the late 60s, while Charles was involved with his future Queen Consort Camilla.
But both couples broke up and Camilla eventually married Parker Bowles.
"It's unclear when their romance wound down, but Anne had no shortage of young men interested in her, among them Mark Phillips, whom she first met in 1968," said royal biographer Sally Bedell Smith.
Despite the potential for drama, Ms Smith said everyone remained on relatively good terms — even when Camilla and then Prince Charles married in 2005.
"Anne and Andrew have remained friends to this day, and he is a godfather of Anne and Mark's daughter, Zara, born in 1981."
Like her brothers Charles and Andrew, Princess Anne's marriage also collapsed in 1992.
Now remarried, this time to Sir Timothy Lawrence, she has largely kept her private life out of the headlines.
Royal writer Phil Dampier predicted in 2019 that the woman once considered "the black sheep" of the family would become a key figure during King Charles's reign.
"She's likely to become a much more important figure," he wrote.
"Unlike her younger brother, she's extremely discreet and not likely to make any faux pas. She's a safe pair of hands."
While Prince Andrew was engulfed in scandal due to his connections to late sex offender Jeffrey Epstein, Anne was the sibling that Charles could rely upon.
She declined royal titles for her children, and forged a strong connection to Scotland — something that could prove vital in keeping the United Kingdom together.
"In the same way that the Queen had Princess Margaret to turn to for most of her life, the King has the Princess Royal," an unnamed royal source told the UK Telegraph.
"There is something quite steadying for him having her around, because they are close and they love to share a joke, but she also absolutely respects the role he inhabits."
As King Charles fulfils his long-held plan to reshape the monarchy as a modern, slimmed down operation, Princess Anne could soon be elevated to a key role.
Could Anne become a counsellor of state?
Since Queen Elizabeth II's passing, reports have emerged that King Charles III wants to shake up the existing counsellors of state.
This royal inner circle are appointed from among the four adults next in succession, who have reached the age of 21, under the 1937 Regency Act.
Among their duties, two or more counsellors of state can be appointed to act in the King's place in the event that he cannot undertake his official duties as sovereign on a "temporary basis due to illness or absence abroad".
As next in line to the throne, Charles served as one of Queen Elizabeth II's counsellors of state and was replaced by Prince Andrew's daughter, Princess Beatrice — a non-working royal — when he acceded to the throne.
Camilla also joined the group after becoming Queen Consort.
Prince William, Prince Harry and Prince Andrew round out the list — though Buckingham Palace has been under pressure for some time to replace the Duke of York and the Duke of Sussex since the pair are not considered working royals.
King Charles is apparently aware of the "incongruity of having a trio of non-working royals" able to step into his shoes and apparently wants the law amended so this group are all working members, the Telegraph reported.
The move would see Prince Andrew, Prince Harry and Princess Beatrice all relieved of their duties as counsellors of state, the newspaper added, with the Earl of Wessex and the Princess Royal possibly elevated to the position.
Princess Anne is currently not a counsellor of state because when she was born, male heirs had first right to the throne over females, and Prince Edward is too far down the order of succession to be considered.
However, if the law were changed to stipulate only working royals hold the position, instead of those highest in the line of the succession, both siblings could be elevated.
With her mother gone, Princess Anne is also likely to fulfil a more symbolic role in the family.
Despite being lower in the order of succession, her decades of experience as a hard-working member of the family mean she is now the House of Windsor's most senior female royal next to Queen Consort Camilla.
And she isn't afraid to offer pearls of wisdom to a younger generation of royals eager to make changes.
Princess Anne has described herself as "the boring old fuddy-duddy at the back" issuing words of warning to her family.
"Nowadays, [this younger generation is] much more looking for, 'Oh let's do it a new way,'" she told Vanity Fair in a profile in 2020.
"And I'm already at the stage, 'Please do not reinvent that particular wheel. We've been there, done that. Some of these things don't work. You may need to go back to basics.'"