The proclamation follows his mother Margrethe’s surprise announcement on live TV on New Year’s Eve that she would abdicate in favour of her oldest son after 52 years on the throne.
It is the first time in nearly 900 years that a sitting Danish monarch has abdicated. People on the streets of the capital said they looked forward to witnessing the “historic” moment when a living monarch will be succeeded by their heir.
The succession was formalised when Margrethe signed the declaration of her abdication during a meeting of the Council of State at parliament. After signing the declaration, the queen rose and gestured to Frederik to take her seat, and said “God save the King” before leaving the room.
Frederik and his wife Queen Mary took the throne at a time of massive public support and enthusiasm for the monarchy in Denmark, recent opinion polls show.
As the first Australian-born Queen in history, Mary has captivated Danes and Australians alike for over two decades.
After the abdication, the new monarch, 55, was proclaimed king by Prime Minister Mette Frederiksen on the balcony of the parliament building, Christiansborg castle, with the words “Long live his majesty King Frederik the 10th”.
Wearing a ceremonial military uniform adorned with medals, Frederik addressed the crowd from the balcony.
“My hope is to become a unifying king of tomorrow. It is a task I have approached all my life. It is a task I take on with pride, respect and joy,” he said.
Visibly moved and several times wiping tears from his eyes, Frederik ended his speech with the words: “United, committed, for the Kingdom of Denmark,” his royal motto, a 500-year old tradition supposed to underpin a new monarch’s reign.
Frederik was joined on the balcony by his Australian-born wife Mary, 51, who is now queen, and their children: Christian, 18, who is the new heir to the throne, Princess Isabelle, 16, and 13-year-old twins Princess Josephine and Prince Vincent.
The royal couple, who met in Sydney during the 2000 Olympic Games, kissed before leaving the balcony amid roaring cheers from the tens of thousands of people who had converged on the capital in close to freezing temperatures.
“They did so well. I think it was so nice that they ended with a kiss, the whole square was oozing with love and joy in that moment,” said one woman who gave her name only as Marie.
The new king and queen take the throne at a time of huge public support and enthusiasm for the monarchy in the nation of nearly six million.
“It brought tears in a joyful way to see him do so well up on the balcony, both with his speech and when Mary came out and held his hands and finishing with a kiss,” said Kasper Wiigh Larsen, 45.
“It has really been worth it to stand here and wait all day,” he said.
Police closed several metro stations in central Copenhagen for security reasons to stop more people from entering the packed streets.
The new king and queen rode by horse carriage through the crowds back to their residence, Amalienborg, a royal complex built in the 1750s and located in central Copenhagen.
The royal family appeared later on the balcony of their residence to greet thousands of people below. The couple will continue to reside with Margrethe, who will retain her title as queen, in Amalienborg albeit in their respective palaces in the octagonal complex.
Margrethe, who had said in the past she would remain on the throne for life, did not give a reason for her decision to step down but said that a major back surgery she underwent in February last year had made her consider her future.
