Margrethe II will be succeeded by her eldest son, Crown Prince Frederik, when she steps down on 14 January.
Denmark’s queen has unexpectedly announced her abdication in her traditional New Year’s Eve speech.
Margrethe II will formally step down on 14 January – exactly 52 years to the day of her ascension to the throne in 1972.
The 83-year-old monarch will be succeeded by her eldest son, Crown Prince Frederik – who will become Frederik X.
Margrethe, who underwent back surgery at the start of this year, said in her speech: “The surgery naturally gave rise to thinking about the future – whether the time had come to leave the responsibility to the next generation.”
With her voice cracking, she said: “I have decided that now is the right time. On 14 January – 52 years after I succeeded my beloved father – I will step down as queen of Denmark
“I leave the throne to my son, Crown Prince Frederik,” she said.
Jesper Steinmetz, the European correspondent for TV 2 Denmark, described the announcement of her abdication as a “total surprise”, telling Sky News it had left Denmark “in shock”.
Margrethe – the eldest child of Denmark’s former monarch King Frederik IX and Queen Ingrid – succeeded her father following his death on 14 January 1972.
She became Europe’s current longest-serving monarch following the death of Queen Elizabeth II in September 2022.
She is also the world’s only queen regnant – as opposed to a queen consort or queen regent who shares her spouse’s title.
In July, Margrethe became the longest-sitting monarch in Denmark’s history.
The record was previously held by 17th-century monarch Christian IV, who, while he technically reigned for 60 years, only ruled for 51 years and six months, as he was a child for the early part of his reign.
Margrethe celebrated her Golden Jubilee in July 2022, with a series of events held across Denmark.
However, she underwent “extensive” back surgery at the start of this year – which meant she was unable to attend King Charles’s coronation in London in May.
Crown Prince Frederik and his wife represented the Danish royal family in her place.
Margrethe also made headlines in September last year after stripping four of her grandchildren of their royal titles.
The move followed in the footsteps of other European monarchies attempting to slim down the number of frontline royals.
The official reason given at the time was to allow the four children, of her youngest son, Prince Joachim, to live more normal lives.
However, the mother of Prince Joachim’s two eldest sons later told Danish media she was “shocked” by the decision.
Danish journalist, Mr Steinmetz, described the announcement of Margrethe’s abdication as a “total surprise”.
“It is a complete shocker,” he told Sky News.
“There was no indication in advance that she was going to announce this, so the nation is in shock.”
Asked why she had decided to abdicate now, he said: “She said in her speech that she had major back surgery earlier this year.
“She recuperated well and is doing fine, but she said that when you are 83 you are not able to do the same things you were when you were younger.
“So I think she just found that the time was right – that is what she said in her New Year speech, that she thought the time was right to pass on the baton to her eldest son.”