When Sophie and Edward tied the knot on June 19, 1999, they had already broken several significant royal barriers.

Having dated Edward for six years, the then Sophie Rhys-Jones was the first royal girlfriend ever to be permitted to stay overnight at Buckingham Palace as an unmarried woman — still a shocking proposition at the time.

What’s more, as the daughter of a tyre salesman from Kent she was, to use criminally old-fashioned parlance, a ‘commoner’ (let us not forget, when he was born, Edward was, by comparison, third in line to the throne).

And the couple’s insistence on not giving up their day jobs — she in PR and he in television production — was equally unheard of in royal circles.

But perhaps most notable was the fact that they were optimistically embarking on married life at a time when Edward’s three siblings — Prince Charles, Prince Andrew and Princess Anne — had all just seen their first marriages sadly end in divorce.

Handout photo provided by Buckingham Palace of the Duke and Duchess of Edinburgh, in the gardens of Bagshot Park, Windsor, who will celebrate their 25th wedding anniversary

The Duke and Duchess of Edinburgh on the balcony at Buckingham Palace during Trooping the Colour at the weekend

File photo dated May 30 2002 of the countess of Wessex and the Earl of Wessex meeting pearly Kings and Queens at Canary Wharf station, London

Britain’s royal family are reunited on Buckingham Palace balcony

File photo dated 26 November 2003 of the Earl and Countess of Wessex leaving Frimley Park Hospital in Surrey with their baby daughter

And yet against the odds, Sophie and Edward — who were made the Earl and Countess of Wessex when they wed but have since been ‘promoted’ to Duke and Duchess of Edinburgh by the King — will tomorrow celebrate their silver wedding anniversary.

In royal circles they are known as a universally happy couple who have barely (certainly not since the notorious ‘Fake Sheikh’ scandal of the late 1990s in which Sophie was duped by an undercover reporter into making indiscreet comments about the then Prince Charles, Tony Blair and William Hague, and subsequently chose to give up her PR business) put a foot wrong.

They have two lovely children, James, now Earl of Wessex, who is currently undertaking his GCSEs and Lady Louise, an English literature student at St Andrews University who, family friends tell me, is turning into a confident young woman.

They plan to celebrate 25 years of marriage in typically low-key style, I can reveal, with a group of close pals at Royal Ascot (and not even in the royal carriage procession).

It is this careful balancing of their positions as full-time working royals with a strong sense of duty, together with their life as partners and parents, that is the secret to their success, say friends.

File photo dated 8 April 2024 of the Duke and Duchess of Edinburgh, on behalf of King Charles III, watching the Changing of the Guard at Buckingham Palace, London

Prince Edward embraces Sophie after she delivered a speech on international women’s day

Duchess of Edinburgh pays sweet tribute to Edward on his birthday

File photo dated 6 May 2023 of (left to right) the Duke of Edinburgh, the Earl of Wessex, Lady Louise Windsor, Vice Admiral Timothy Laurence, the Duchess of Edinburgh, Princess Charlotte, the Princess of Wales, Prince Louis, the Prince of Wales and the Pages of Honour including Prince George (far right) on the balcony of Buckingham Palace, London, following the coronation

‘They are a real team,’ one life-long friend of the couple tells me. ‘There’s an equilibrium in the relationship, neither one is jealous of the other. In fact they take great pride in the other’s achievements.

‘When Sophie undertook a 450-mile cycling challenge a few years ago from Edinburgh to London there was no one prouder than the prince, I can tell you.’

According to Sophie, 59, who paid a remarkable public tribute to her husband on his 60th birthday in March, it’s also the fact that he is ‘the best of the fathers and the most loving of husbands’.

She sweetly described Edward as her ‘best friend’ — and unhesitatingly admitted that she still fancies him in a uniform.

For Edward’s part, in an exclusive interview with me to mark his landmark birthday, he notably came alive as he discussed his wife.

‘Well, you need a really good supportive network in this and family is incredibly important. I am just very, very lucky that Sophie is a brilliant, brilliant person in her own right,’ he told me, smiling from ear to ear.

Friends say the prince has never taken for granted what Sophie took on when she married him, after they famously first met at a ‘real tennis’ tournament she was doing the PR for and he was playing in.

File photo dated 19 June 1999 of Prince Edward, the youngest son of Britain’s Queen Elizabeth II, and his bride Sophie Rhys-Jones leave St. Georges’s Chapel in Windsor Castle following their marriage

The couple attend a D-Day Remembrance service for veterans in Alrewas, Staffordshir

Prince Edward waves at crowds on the day of his wedding to Sophie on June 19, 1999

Moment Prince Edward sweetly acknowledges wife Duchess Sophie

Their close friend Mark Foster-Brown, who has known Edward since their days at Cambridge University (and was also a guest at the tournament when they first met) agrees, adding: ‘I just feel that there is a particular pride in him at what she does and how she does it. That’s very bonding, it would be in any marriage, and it certainly is in theirs.’

Sophie has become an acclaimed campaigner for men and women who are victims of sexual violence in war and recently became the first British royal to travel to Ukraine to highlight this untold story of the current conflict.

Edward, meanwhile, has taken on the mantle of his late father, not just in name but in many of the public duties he once undertook, particularly with the Duke of Edinburgh’s Award scheme.

While the couple would insist they aren’t doing anything particularly different nowadays — it’s just that people have started to notice it more in a slimmed-down monarchy — there’s little doubt their star is in the ascendance.

Outside work they are both very much country sorts, adoring their dogs, walking and riding.

They’re also keen skiers. Edward, in particular, is ‘irritatingly good’ and utterly ‘fearless’, says one friend. Sophie did a season on the slopes after leaving school and isn’t far behind.

The couple are known too to enjoy ‘bucket and spade’ family holidays in places such as the Isles of Scilly.

One family friend who has holidayed with them recalls a member of the public once coming up to Edward to tell him that he was a ‘dead ringer’ for the Queen’s youngest son — clearly not thinking for a second that the man queuing up to get supplies in the Co-op could ever have been him.

Above all, Sophie and Edward laugh a lot.

‘There is always something for them to giggle about,’ says a pal.