Philip was a no-nonsense, quizzical, controversial man of strong character, who saw it as his duty never to let the monarch down.
But he refused to shy away from telling his wife exactly what was what.
Lord Charteris, the monarch’s former private secretary, once recalled: “Prince Philip is the only man in the world who treats the Queen simply as another human being.
“He’s the only man who can. Strange as it may seem, I believe she values that,” he told royal writer Gyles Brandreth.
The death of her greatest supporter and husband of 73 years at the age of 99 in 2021 was devastating for the Queen.
Philip was the monarch’s rock and he dedicated himself to royal duty throughout the decades, retiring only when he was 96.
He had lived through the ups and downs of her life and reign, from the joys and sorrows their family brought to the unique experiences and challenges that befell the Queen as head of state.
Their long-lasting marriage was put down to their compatibility.
They shared interests and had the same dutiful royal training.
Both loved horses and the outdoor life; both were undemonstrative by nature, regarding displays of emotion as something to be kept private.
Yet in character, the Queen and Philip were markedly different.
She was passive, cautious, non-confrontational and conventional; he was more outspoken, adventurous, tempestuous and active.
Their partnership was a traditional one and the Queen grew up in a world where it was the man who was in charge behind closed doors.
A friend of the royals once told biographer Sarah Bradford: “He shouts at the Queen sometimes, like he shouts at other people, and she doesn’t seem to mind.
“It’s as if she thinks that’s how husbands behave.”
There were moments when Philip’s bluntness embarrassed the Queen, but she was not averse to telling him to “Shut up”.
She knew how to handle him and would retort: “Oh, Philip, do shut up. You don’t know what you’re talking about.”
When he shouted at her in private, she would calmly ignore it.
The Queen clearly adored the duke.
During public engagements, she would sometimes be seen waiting for him to catch up with her as he lingered behind, entertaining the guests.
“Where’s Philip?” she would ask and, on catching sight of him walking towards her, would give a small chuckle and flash him a beaming smile.
In the early days of their marriage, Philip was sometimes strident and, according to close friends, Elizabeth would not fight back.
Later she learned to resist and, in the end, the couple achieved a kind of harmony, said the Queen’s biographer, Ben Pimlott.
But their domestic relationship could perhaps best be illustrated by an anecdote recounted by Lord Mountbatten.
Philip, who had a record of minor motoring accidents, was driving his wife and Lord Mountbatten to Cowdray Park.
The Queen, worried about the speed at which Philip was going, started to tense herself and draw in breath.
Eventually her husband turned to her and barked: “If you do that once more I shall put you out of the car.”
She stopped immediately.
When they arrived, Lord Mountbatten asked her: “Why didn’t you protest? You were quite right, he was going much too fast.”
The Queen looked puzzled and replied: “But you heard what he said.”
The difficulties facing the royal family since 1992, the Queen’s “annus horribilis”, were said to have brought the couple closer together.
The duke, who had mellowed with age, became noticeably more considerate and supportive.
“He’s unsung for the total support he gives to the Queen,” a Royal Household insider once told author Bradford. “They’re like Darby and Joan now – it’s very sweet really.”
While on honeymoon Princess Elizabeth wrote to the Queen Mother, in letters seen by biographer William Shawcross, and declared: “Philip is an angel – he is so kind and thoughtful and living with him and having him around all the time is just perfect.”
Philip in turn wrote to tell his mother-in-law of his deep love for his new wife.
“Lilibet is the only ‘thing’ in the world which is absolutely real to me and my ambition is to weld the two of us into a new combined existence that will not only be able to withstand the shocks directed at us but will have a positive existence for the good,” he said.
On the Queen’s accession, Philip watched her become the single most important woman in the country and was furious to discover that his own children would not be allowed to take his name.
He later won a part-concession when in 1960 it was announced that the Queen’s descendants, when they needed a surname, would use Mountbatten-Windsor.
He devoted his married life to supporting the Queen, giving up his naval career to be by her side.
At the start of her reign, he helped her in particular with her public speaking, encouraging her to lower her voice when she spoke.
He was incredibly protective of his wife and would berate photographers who got too close.
A cruise of Commonwealth countries in 1956 took Philip away from the Queen for four months, prompting rumours of a rift between them. But there was no evidence that all was not well.
To celebrate their golden wedding anniversary in 1997, the duke praised his wife for her abundance of tolerance.
“I think the main lesson that we have learnt is that tolerance is the one essential ingredient of any happy marriage,” he said.
He added: “It may not be quite so important when things are going well, but it is absolutely vital when the going gets difficult.
“You can take it from me that the Queen has the quality of tolerance in abundance.”
The Queen spoke of him fondly in return.
“All too often, I fear, Prince Philip has had to listen to me speaking,” she said.
“Frequently we have discussed my intended speech beforehand and, as you will imagine, his views have been expressed in a forthright manner.
“He is someone who doesn’t take easily to compliments but he has, quite simply, been my strength and stay all these years, and I, and his whole family, and this and many other countries, owe him a debt greater than he would ever claim, or we shall ever know.”
In 2007, they reached 60 years together, celebrating their diamond wedding anniversary.
To mark The Queen and The Duke of Edinburgh's 70th Wedding Anniversary, new photographic portraits have been released worldwide. pic.twitter.com/Jl6elndhFe
— The Royal Family (@RoyalFamily) November 18, 2017
In 2012, they marked their blue sapphire anniversary – 65 years – and in 2017 passed the rare milestone of 70 years of marriage – their platinum wedding anniversary.
The duke’s death in April 2021 occurred during lockdown in the midst of the coronavirus crisis.
Before the pandemic, Philip had been occupying himself after his retirement mostly at his cottage, Wood Farm, in the sanctuary of the Sandringham estate, while the Queen was more than 100 miles away in London or Berkshire carrying out her official duties.
The couple had always enjoyed spending time together but also retained their separate interests.
The duke kept himself busy reading, writing and painting, while the Queen enjoyed riding her fell ponies in Windsor Home Park and speaking with friends.
The Covid-19 crisis meant they spent more time under the same roof together during lockdown than they had in many years, giving them the chance to reconnect.
Throughout their marriage, there were rumours that Philip had strayed, although none was ever proven.
The Queen remained smitten with the man she fell in love with when she was 13.
Observers said you could see it in her eyes when she watched the duke compete at carriage driving.
From the sidelines, she would get excited, bite her nails nervously and take pictures on her old-fashioned camera of the man who, as a tall, dashing naval cadet, captured her heart all those years ago.