A new official portrait of the Queen and Prince Philip has been released in honour of their platinum wedding anniversary, which marks 70 years of marriage.

The three photos, taken by Matt Holyoak earlier this month, shows the royal couple in the White Drawing Room at Windsor Castle.

The Queen is seated, smiling, alongside the standing Duke of Edinburgh in one shot, while another shows the pair in a more sombre attitude, standing side by side. In the third, more intimate photograph, the two are looking at one another as though sharing a joke.

There will be no public commemoration of the longest marriage in British royal history. “Close family and friends are gathering with the couple at Windsor Castle for a special private dinner on Monday evening,” The Guardian reports.

The pair first met in 1939, when the Queen was a teenage princess and the Duke of Edinburgh was a naval cadet. They later began a courtship that was initially frowned upon by the Queen’s parents, who considered Philip - a minor member of the ousted Greek royal family - small fry in comparison to their daughter.

Despite the royal family’s initial discomfort, Princess Elizabeth and Philip Mountbatten married on 20 November 1947. They went on to have four children - Charles, Anne, Andrew and Edward.

Although only fleeting glimpses of their private lives together have made it into the public domain, the Queen and Prince Philip’s marriage has had ups and downs like any other.

Despite seven decades of seemingly serene married life, “rumours of [Prince Philip’s] alleged affairs have been rife” from the start of the marriage, royal biographer Ingrid Seward writes for the Daily Mail.

However, no credible evidence has ever surfaced for any illicit encounters, and the Duke himself has given the gossip short shrift, joking that he is too closely supervised by security to get away with any infidelity.

Other marital issues are better documented. “In the early days Philip struggled with constantly being in the Queen’s shadow,” the Daily Express reports.

The Duke reportedly bristled at being required to walk behind his wife at official functions, and railed against being the “the only man in the country not allowed to give his name to his own children”.

However, over time the prince consort has adapted to his role, channelling his energy into charitable programmes including the Duke of Edinburgh Award, and demonstrating fierce loyalty to the Queen.

The Duke has remarked that “tolerance” is the secret to a happy marriage. “You can take it from me, the Queen has the quality of tolerance in abundance,” he said.

For her part, the Queen has echoed her husband’s devotion. As the pair celebrated their golden anniversary in 1997, the Queen paid a touching tribute to her consort, whom she called her “strength and stay”.

“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,” she said in a rare public profession of affection.

While the prince’s forthright manner and earthy sense of humour have occasionally landed him in hot water, for the Queen they provide a welcome antidote to the reverence with which she is treated elsewhere, according to her former private secretary, Lord Charteris.

“Prince Philip is the only man in the world who treats the Queen simply as another human being,” he said.