Frederik X is proclaimed the new king of Denmark after his mother Queen Margrethe II abdicates

Denmark’s prime minister proclaimed Frederik X as king on Sunday after his mother Queen Margrethe II formally signed her abdication, with massive crowds turning out to rejoice in the throne passing from a beloved monarch to her popular son.

Margrethe, 83, is the first Danish monarch to voluntarily relinquish the throne in nearly 900 years. Many thousands of people gathered outside the palace where the royal succession took place, the mood jubilant as the Nordic nation experienced its first royal succession in more than a half-century, and one not caused by the death of a monarch.

Denmark’s monarchy traces its origins to 10th-century Viking king Gorm the Old, making it the oldest in Europe and one of the oldest in the world. Today the royal family’s duties are largely ceremonial.

Margrethe signed her abdication during a meeting with the government at the Christiansborg Palace, a vast complex in Copenhagen that has been the seat of Danish power for centuries. It now houses the Royal Reception Rooms and Royal Stables as well as the Danish Parliament, the prime minister’s office and the Supreme Court.

Prime Minister Mette Frederiksen next proclaimed Frederik king from the balcony of the palace before the cheering crowd.

Frederiksen read the proclamation three times, which is the tradition, as Frederik stood beside her wearing a ceremonial military uniform adorned with medals. He was then joined on the balcony by the new, Australian-born Queen Mary and the couple's four children, and the crowd spontaneously sang the national anthem.

“My hope is to become a unifying king of tomorrow," Frederik said. “It is a task I have approached all my life.”

It is the custom for each new sovereign to adopt a royal motto as a guiding principle for their reign, and Frederik's is: “United, committed, for the kingdom of Denmark.”

“I want to return the trust I meet," the new king said. “I need trust from my beloved wife, you and that which is greater than us.”

Frederik kissed Mary, the queen, who wore a white dress with a sash over one shoulder, and another great cheer rose from the crowd.

They then left Christianborg Palace in a horse-drawn coach as church bells rang out, and headed to their Amalienborg residence, where they once again appeared before people cheering and waving the nation's flag of a white cross on a red background.

Frederik, who was visibly moved, placed both hands on his heart in a gesture of thanks.

The abdication document was earlier presented to Margrethe as she sat at a massive table covered in red cloth around which royals and members of the Danish government were seated. Frederik sat beside her.

After signing it, Margrethe, dressed in a magenta skirt suit, rose and gestured to Frederik to take her place. “God save the king,” she said as she left the room using a cane for support.

The abdication leaves Denmark with two queens: Margrethe keeps her title, while Frederik’s wife becomes Queen Mary. Frederik and Mary’s eldest son Christian, 18, has become crown prince and heir to the throne.