The Queen’s last summer was one of her happiest of recent years, entertaining a string of family and friends at Balmoral.

Her Highland estate – every purple-hued sprig brimming with memories of her beloved Philip – had been a huge source of comfort after the most difficult of times.

One source with close links to the Royal Household told me recently that she had not been suffering from any chronic condition. Another said: ‘She’s lost a lot of weight and has been feeling all the aches and pains that a 96-year-old woman would be expected to feel and has suffered terrible problems with her sore feet.’

But there is no doubt that Her Majesty’s sudden frailty and health decline came as a shock to many of those around her.

Moreover, the loss of her husband of 73 years combined with the drama over Harry and Meghan’s acrimonious departure from the family and the deeply troubling allegations swirling around Prince Andrew took a ‘deep emotional toll’ over the past two years.

One insider told me recently: ‘Her Majesty was always discreet but you can see with your own eyes what a toll it has taken on her emotionally. It brought her great heartache and has not been an easy time.’

Still, as the Queen arrived in Balmoral at the end of July – moving firstly into the smaller, more comfortable seven-bedroom Craigowan Lodge on Royal Deeside, before transferring to Balmoral Castle a mile away on August 9 – the Highland air seemed to bring a sense of comfort and relief.

Accompanying the Queen were the handful of loyal staff who vowed to stay with her until the end.

Beloved bolthole: Balmoral Castle, where the Queen spent her last hours, was a huge comfort to her during her lifetime

Her 6ft 4in Page of the Backstairs Paul Whybrew – ‘Tall Paul’ – and Barry Mitford, her Serjeant-at-Arms were with her, as always. The two men were her regular companions, bringing her the Racing Post each day and companionably sitting with her to watch her favourite sport on the television.

Also by her side was Angela Kelly, the Liverpudlian dock worker’s daughter who rose to become her right-hand woman with the title of Personal Assistant, Adviser and Curator to Her Majesty The Queen. Fiercely protective Angela – wittily dubbed ‘AK47’ – did not leave her side.

‘She’s been wrapping the Queen up in cotton wool,’ a source told me over the summer. ‘She’s been very overprotective and ensuring that Her Majesty hasn’t been doing too much.’

One source with intimate knowledge of the goings-on at Balmoral told me that the Queen spent her last few weeks enjoying the country life she adored.

She and Philip were at their happiest in the Highlands, where they enjoyed the existence of a fairly normal married couple – it was no accident that she chose to release a picture of them together there after his death.

Indeed, the Queen was seen only a few weeks ago walking her corgis in the gardens, slowly and cautiously (like many elderly people she had a fear of falling over, particularly in public, which is one of the reasons she was so careful about what engagements she chose to undertake in public) but out in the fresh air nonetheless.

Her Majesty arriving at Balmoral Castle for the start of her summer break on July 21

She and Philip were at their happiest in the Highlands, where they enjoyed the existence of a fairly normal married couple

The Queen spent her final hours in the bosom of her family, at the place where she spent so many happy times with her beloved Philip

The family have been regularly visiting the Scottish castle for more than half a century

A ‘stream’ of family came to see her, most recently the Duke and Duchess of Cambridge and their lively three youngsters who ‘Gan Gan’ – as the children called their great-grandmother – found such a tonic. The notable absentees were the Duke and Duchess of Sussex, a story in itself.

The late monarch was particularly comforted by the regular presence of Prince Edward and his wife, Sophie, whom she adored like a second daughter, and her late sister Princess Margaret’s two children, Lady Sarah Chatto, and the Earl of Snowdon, of whom she was so fond.

‘It’s been a very typical and jolly summer at Balmoral, lots of walks and picnics and BBQs. It has followed the pace long set by the Queen and the late Duke of Edinburgh. Obviously the Queen hasn’t been present throughout but she has taken part and been seen,’ a source said at the time.

Another royal source who encountered the Queen just days ago described her to me as being in ‘genuinely good spirits’. ‘I know you would expect me to say that but she really was,’ they said, suggesting that her decline overnight on Wednesday was sudden.

On Tuesday she met not just her outgoing and incoming prime ministers but undertook an investiture and some light paperwork.

And yet, behind the scenes, concern was rapidly growing among Buckingham Palace’s most senior staff as to how much the Queen could have been expected to do when she returned to Windsor Castle.

‘They were already heavily pacing her and warning people that it had now come to the point that if she needed to do X, she couldn’t do Y, and that engagements were the exception not the rule.

‘But there has been an unmistakable shift in the strength and urgency of talks in recent weeks,’ my source said at the time.

The Queen attends an audience with Switzerland’s president at Windsor Castle on April 28

(Left to right) The Duchess of Cornwall, the Prince of Wales, Queen Elizabeth II, the Duke of Edinburgh, and Duke and Duchess of Cambridge at Buckingham Palace on December 8, 2016

The Queen was seen only a few weeks ago walking her corgis in the gardens – something she has been doing for decades

Prince William is now heir to the throne of the United Kingdom after Prince Charles’s accession following the death of Queen Elizabeth II. Above: The Queen on the Buckingham Palace balcony with Prince Charles, Prince William and his children, Prince George and Princess Charlotte during the Platinum Jubilee Pageant in June

Indeed, I can reveal that over the last fortnight there were high-level discussions between senior courtiers at Buckingham Palace and Clarence House – the likes of her private secretary Sir Edward Young, his opposite number at Clarence House, Sir Clive Alderton, and Master of the Household, Sir Tony Johnstone-Burt – about exactly what operational duties the Queen would have been able to discharge when she returned to Windsor in the autumn, if any.

‘It had become abundantly clear to everyone that, while mentally agile, she physically wasn’t up to the strain of the role and there have been serious discussions about what duties she would, if at all, be able to discharge,’ my source said at the time.

‘The mechanics were already being drawn up to ensure the Prince of Wales could take over most of her day-to-day responsibilities.’ In other words, a full regency in all but name.

Significantly, on Tuesday night, I received a call from a friend of a friend telling me: ‘It doesn’t look like the Queen will be returning from Balmoral in October. Everyone at Windsor is deeply worried about her.’

It had long been suggested, I should explain, that after the death of the Duke of Edinburgh, the Queen would move almost full-time to Scotland.

It’s something I know was discussed within the Royal Household but was always understood to be unlikely – for practical reasons as much as anything. Buckingham Palace refused to comment.

Such matters have now been overtaken by yesterday’s events. But we can surely all take a crumb of comfort that the Queen spent her final hours in the bosom of her family, at the place where she spent so many happy times with her beloved Philip, gazing over the Scottish Highlands that she held so dear.