King Harald and Queen Sonja of Norway both turn 80 this year, so they held a lavish soiree to celebrate and invited Europe’s royals to party with them in Oslo.

The two-day celebration commenced with a formal dinner at the Royal Palace on Tuesday night and continued on Wednesday with a lunchtime cruise, followed by a gala banquet dinner at the Oslo Opera House.

Europe’s royals proved one thing – they sure know how to party.

On Wednesday, royal guests – including Crown Princess Mary and Crown Prince Frederik of Denmark – poured into Oslo in all their finery, with the women resplendent in tiaras and designer gowns.

Denmark’s royal family managed to steal the spotlight from the birthday boy and girl by making a major entrance on their 78-metre royal yacht, Dannebrog.

Next, the entire party – including royals from Greece, the Netherlands, Spain and more – took themselves to the balcony of the Palace to wave to the public.

Waiting crowds sang Happy Birthday to their king and queen, while their son, Crown Prince Haakon, and his wife, Crown Princess Mette-Marit, were caught doing a playful jig.

The couple’s 11-year-old son, Prince Sverre Magnus, was photographed “dabbing” – a viral dance move that originated in the US hip-hop community.

The hijinks continued at the dinner, where Prince Haakon pranked attendees by shaving his substantial beard off midway through the meal.

Meanwhile, his father delivered a toast peppered with wisecracks about growing older.

“A wise man – that’s not me – once said, ‘Inside every old person is a young person wondering what happened’,” King Harald joked to much laughter.

Prince Haakon’s quick mid-dinner makeover. Photo: Getty

Although Queen Sonja made a bold statement in her fluorescent lime green gown, most of the attendees played it safe sartorially.

However, one risk taker was Desirée Kogevinas, the daughter of Swedish Countess Madeleine Bernadotte, who stood out from the pack of pastel and lace gowns by going bra-less beneath her daring, one-shoulder slinky sheath with bold gold headpiece.

Desirée Kogevinas braved the chilly temperatures in Oslo in a bold red gown. Photo: Getty

King Harald marked his 80th birthday on February 21, while Queen Sonja will celebrate hers on July 4.

The king met Queen Sonja, a commoner, in 1959 and the pair kept their relationship a secret for almost a decade due to fear of royal disapproval.

King Harald threatened to never marry if he wasn’t allowed to wed Queen Sonja.

Thankfully, they eventually walked down the aisle in 1968, after King Harald’s father, King Olav, finally granted them his permission.

“Celebrating the 80th anniversary is not something we take for granted,” King Harald said.

“We are blessed with good health, blessed with the love of the family, blessed with loyal friends who have stood by our side through ups and downs, and blessed with a meaningful life in service to our country and our people.”

“Skål!” he concluded, using the Norwegian word for ‘cheers’.