Why did Kate Middleton and Prince William miss Denmark’s Prince Christian’s 18th birthday party? Royal expert reveals why couples don’t party with their European cousins

It was one of the most glamorous events on this year’s social calendar, with royals from across Europe gathering in Copenhagen to celebrate Prince Christian’s 18th birthday.

The glitzy gala at Christiansborg Castle was an opportunity for future kings and queens to mingle, but senior members of the British royal family were nowhere to be seen.

This isn’t the first time the likes of King Charles, Queen Camilla, the Prince and Princess of Wales, the Princess Royal and the Duke and Duchess of Edinburgh have been absent from a party hosted by a European royal family.

In September, Sweden’s King Carl didn’t show up.

Dickie Arbiter, the former press secretary to the late Queen Elizabeth II, told FEMAIL it is likely a busy schedule and the downsized monarchy is to blame for the lack of British royals at their European counterparts’ festivities.

Yesterday, glamorous guests such as Princesses Victoria of Sweden, Catherine Amalia of the Netherlands and Elisabeth of Belgium wore stunning tiaras and dazzling gowns as they celebrated the 18th birthday of the future King of Denmark.

Prince Christian is a four-time great-grandson of Queen Victoria and a distant cousin of Prince William. His grandmother, Queen Margrehte, was the third cousin of the late Queen Elizabeth and the couple had a warm relationship.

But instead of traveling to Denmark for the lavish occasion, the Prince of Wales, 41, traveled to France with his son Prince George, 10, to watch Wales take on Argentina in the Rugby World Cup quarter-final on Saturday.

The Princess of Wales was also at the Rugby World Cup on Sunday to watch England’s quarter-final victory over Fiji at the Stade de Marseille.

It is unclear whether Kate and William – or any other high-ranking British royal – were invited to Prince Christian’s 18th birthday party.

But Dickie has said it is unlikely an invitation would have been accepted due to the British royal family’s busy schedules.

He said: ‘Royal diaries are generally completed a good six to seven months in advance.

‘There are small gaps to accommodate last minute arrangements, as we saw this weekend with The Prince of Wales during the Wales Rugby World Cup quarter-final and The Princess during the England match.

‘The British royal family is not picky, busy, yes. There are only eleven working royals, all with very full schedules and even royals are allowed to have free time.

‘From the Golden Jubilee of King Carl

‘In the past, the late Queen, who was of a similar generation to the Norwegian, Swedish and Danish monarchs, would more than likely have received an invitation and, although not present herself, would have asked one of her relatives to represent her , depending on the nature of the assignment.’

He added: ‘I believe that the British public in general would rather see the royals at work, both in Britain and abroad, than attending birthday celebrations.’

Sometimes the British royals can show up for the festivities of other royal households; Prince Edward and Sophie attended the wedding of Prince Carl Philip of Sweden and Princess Sofia in 2015.

More recently, the Prince and Princess of Wales attended Crown Prince Hussein’s lavish wedding to Rajwa Al-Saif in Jordan in June.

Guests at last night’s gala included Princess Mary of Denmark, Princess Victoria of Sweden and Princess Mette-Marit of Norway, who all looked straight out of a fairy tale as they attended the glamorous party at Christiansborg Palace.

The birthday boy’s mother, Mary, 51, who is married to Prince Frederik, the heir apparent to the Danish throne, put on a dazzling show in the diamond tiara she wore on her wedding day in 2004.

Looking effortlessly elegant, the Australian-born mother of four opted for a gem-encrusted blue dress by Danish designer Jesper Høvring and a pair of glittering diamond earrings.

Sweden’s Victoria, 46, heir to her country’s throne, looked equally radiant in a cream Elie Saab dress with a square neckline that showed off her statement diamond necklace.

Wearing a pair of diamond earrings and a statement tiara to complete her look, the princess attended the occasion with her husband Prince Daniel, 50, and her 11-year-old daughter, Princess Estelle.

Victoria and Estelle weren’t the only glamorous mother and daughter duo at the gala, with Crown Princess Mette-Marit of Norway, 50, and her daughter Princess Ingrid Alexandra, 19, wearing matching blue dresses and sparkling tiaras.

They were joined by Princess Catherine-Amalia of the Netherlands, 19, and Princess Elisabeth of Belgium, 21.

Catharina-Amalia looked stylish in a hooded dress from Essentiel Antwerp, with her long hair down and pinned with a diamond tiara.

Elisabeth, meanwhile, looked every inch a princess in a cream-colored sleeveless dress from Belgian couture brand Natan, which she paired with matching gloves.

Queen Margrethe II of Denmark, whose half-century reign makes her Europe’s longest-serving monarch, is not to be outdone by the younger royals. She turned heads in a bright red dress and the Pearl Poire Tiara.

Other photogenic guests included Crown Prince Haakon of Norway, Crown Prince Frederik of Denmark and Princess Benedkeek of Denmark.

The party included hundreds of wealthy guests from all over Europe, such as Queen Anne-Sophie of Greece, Crown Prince Pavlof of Greece and Crown Princess Marie-Chantal of Greece.

Prince Joachim, meanwhile, attended his cousin’s party, perhaps showing that Denmark’s royal title battle is well and truly behind him – after criticizing his mother Queen Margrethe’s decision last year to give his children their prince and princess titles.

He was accompanied at the gala by his wife Princess Marie and their children, Count Henrik of Monzepat and Countess Athena of Monpezat. Count Felix of Monpezat, Joachim’s second eldest son from his first marriage, was also present.