The Queen and Prince Philip's incredible love story in 20 touching photos

The Queen sadly mourned the death of her beloved husband, the Duke of Edinburgh, in April. Saturday marked a difficult day for the monarch as she would have celebrated her 74th wedding anniversary with Prince Philip.

The Queen and the Duke went through incredible milestones during their marriage and so, to honour their union, we've rounded up the couple's sweetest moments throughout their many years by each other's side…

READ: Prince Philip's most memorable quotes and witty one-liners

Buckingham Palace released a poignant photo of the Queen and Prince Philip relaxing as they enjoyed a picnic on the Balmoral estate, which was taken by the Countess of Wessex in 2003.

The Duke lies back on a rug, propping himself up on his left elbow and has jauntily placed his hat on his right knee. Beaming at the camera, the Queen, dressed in a tartan skirt, blouse and cardigan and a string of pearls, also sits on a rug.

WATCH: The Queen and Prince Philip's 1947 wedding

When the Queen met her dashing war hero Prince Philip of Greece and Denmark, she was a young Princess Elizabeth, heiress to the British throne.

The couple were the William and Kate or Harry and Meghan of their day, with every stage of their courtship eagerly followed by an adoring public.

After tying the knot on 20 November 1947, the Princess described her husband in letters to her parents and her cousin as "an angel" and "the best and nicest man in the world". Meanwhile, Philip said ahead of the wedding: "I am sure that I do not deserve all the good things that have happened to me… to have fallen in love, completely and unreservedly."

MORE: 20 of Prince Philip's sweetest family moments with his children, grandchildren and great-grandchildren

Elizabeth first set eyes on Philip when she was just a teenager, while touring the British naval academy where he was training. A 6ft blue-eyed Adonis prone to irreverent jokes, he exuded confidence and charm. From that time on, "she never thought of anyone else," said the Prince's cousin, Lady Pamela Hicks.

The Queen's cousin Margaret Rhodes also revealed: "I've got letters from her saying, 'It's so exciting. Mummy says that Philip can come and stay.' She was truly in love from the very beginning."

When Philip returned from the Second World War eight years later, the pair's courtship began in earnest. But it took some time for Philip to be accepted by the establishment, because his family was exiled from Greece and without land or fortune.

Elizabeth's devotion never wavered and in July 1947, their engagement was announced. Here, the couple pose at Buckingham Palace shortly before their grand wedding ceremony.

MORE: Prince Philip: a look back on his 70 years of service to the Queen

The royals smile at each other during a walk on their honeymoon in Broadlands, Romsey, Hampshire in 1947.

Writing to his mother-in-law, Philip sweetly said in a letter: "Cherish Lilibet? I wonder if that word is enough to express what is in me."

MORE: 14 heartwarming photos of Prince Philip as a doting grandfather

Prince Philip leans over the Queen's shoulder as they look at their wedding photos together while on their honeymoon. 

MORE: Meet the Queen's adorable great-grandchildren - the next generation of the royal family

The Queen waves with her husband on her Coronation Day from the balcony of Buckingham Palace in 1953. 

MORE: Prince Charles' mishap with the Queen's coronation crown revealed

The couple smile and play with their young children, Prince Charles and Princess Anne, back in August 1951. 

MORE: Prince Philip's incredible wedding gift to the Queen revealed

The royal couple look out of the window with a young Prince Charles and Princess Anne. 

MORE: The story of how the Queen's wedding tiara broke back in 1947 revealed

The pair stroke a horse while visiting a farm on the Balmoral estate in 1972, the year of their Silver Wedding anniversary. 

The royal couple with their four children Princess Anne, Prince Andrew, Prince Edward and Prince Charles in 1972.

In that year, the Queen gave her thoughts on family life, saying: "If I am asked what I think about family life after 25 years of marriage, I can answer with equal simplicity and conviction, I am for it."

The couple chat animatedly to each other during a visit to Durban, South Africa in the nineties. In 1997, Philip revealed the secret to their marriage, saying: "Tolerance is the one essential ingredient in any happy marriage... The Queen has the quality of tolerance in abundance."

To celebrate their Golden Wedding anniversary in 1997, the couple were joined by their family at a Royal Gala, where the Queen fittingly wore a gold dress.

Sweetly marking the occasion, the monarch said of her husband: "He is someone who doesn't take easily to compliments. But he has, quite simply, been my strength and stay all these years. I and his whole family, in this and many other countries, owe him a debt greater than he would ever claim or we shall ever know."

The royals still look very much in love while celebrating their Diamond Wedding Anniversary in 2007. They returned to their honeymoon spot in Broadlands, Hampshire for the photoshoot. 

On the occasion of their Diamond Wedding Anniversary in 2007, the Queen and Prince Philip posed for a beautiful portrait with their four grown-up children at Clarence House.

The couple share a laugh as they say goodbye to the Irish President Michael D. Higgins and his wife Sabina at Windsor Castle in 2014. 

The royal pair show their Team GB spirit as they watch the England vs Wales women's hockey match for the 20th Commonwealth Games in 2014. 

The Queen and Prince Philip share a blanket in 2015 as they watch the Braemar Gathering in Scotland, an annual event in Cairngorms National Park. 

The Queen and Prince Philip surrounded by family on the balcony of Buckingham Palace as they celebrate Her Majesty's 90th birthday in June 2016. 

Princess Eugenie has said of her grandparents: "They are the most incredibly supportive couple to each other. I think he is her rock really and she is his."

In celebration of their 70th wedding anniversary, the Queen and Prince Philip, pictured here at Royal Ascot, posed for a series of official portraits. 

The family celebrated with a black-tie, wedding anniversary dinner at Windsor Castle.

"I would love to know their secret. They are the most lovely couple, and I hope Catherine and I have that sort of future ahead of us," Prince William has previously said.

Prince Philip was always present for special family occasions, such as royal weddings. He joined the Queen at grandson Prince Harry's wedding to Meghan Markle in May 2018 (pictured), and for granddaughter Princess Eugenie's nuptials to Jack Brooksbank in October 2018. 

MORE: How Princess Eugenie and Zara Tindall paid the ultimate tribute to Prince Philip before his death