After the surprise abdication of his mother Queen Margrethe II, Crown Prince Frederik of Denmark will ascend to the throne on 14 January.
A married father-of-four and passionate environmentalist, the 55-year-old crown prince speaks four languages and has recently stepped up his royal duties.
But the man fond of rock concerts who was once dubbed the “party prince” didn’t always appear to be prepared to take over the reins of Europe’s oldest ruling monarchy.
Here, Sky News looks at the future king of Denmark – and how his reign might look.
Queen Margrethe’s eldest son, Crown Prince Frederik was always destined for the throne.
But as a young man in the 1990s, he developed a reputation for being a “party prince”.
He was said to have matured during his time at the University of Aarhus, where he graduated in political science.
As part of his course, he spent some time studying at Harvard University in the US between 1992 and 1993.
His military education began in 1986 in the Queen’s Life Guard regiment.
In 2010, he was appointed as a commander in the navy and colonel in the army and the air force.
Crown Prince Frederik remains active in his country’s defence forces.
Preparing to be king
Marie Rønde, royal correspondent for Danish broadcaster TV2, said Crown Prince Frederik was not always “prepared” for his future role as monarch.
She told Sky News: “He’s talked about it himself that when he turned 18, he was not at all prepared for what came to him at that point.
“He’s used a lot of time getting prepared – like getting used to the fact that this is the task of his life and he’s worked a lot on that.
“I don’t know if you would call him a party prince today, I think he’s changed a lot, but that’s what he was at that time.”
In recent years, the prince – who also speaks English, French and German – has taken on more responsibilities, particularly during Queen Margrethe’s recent ill health.
Ms Rønde said: “A year ago she had back surgery (and) he took over a lot of her work.
“He said that he was like his mother’s ‘wingman’.
“He’s had a long military education and he’s fond of rock music, (he) goes to concerts and festivals, and he’s very into sports events. So in that way, he’s very different from his mother.”
Prince Frederik is the eldest child of Queen Margrethe and Prince Henrik of Denmark, who died in 2018.
His younger brother, Prince Joachim of Denmark, is one year his junior.
In 2022, Queen Margrethe stripped Joachim’s four children of their royal titles, saying it was “necessary future-proofing of the monarchy”.
The move did not affect Crown Prince Frederik’s children, who all retain their titles, nor did it impact the line of succession.
Frederik first met his wife, Mary, crown princess of Denmark, at a bar during the Sydney Olympics in 2000.
The Australian-born princess worked in advertising before meeting the prince.
They were married in 2004 and the couple have four children – 18-year-old Prince Christian, 16-year-old Princess Isabella, and 12-year-old twins Prince Vincent and Princess Josephine.
Ms Rønde believes the crown princess will be a “very strong queen”.
She said: “It’s been clear all these years that his wife, Crown Princess Mary, has always been very supportive of him and she’s been by his side – like you see with Queen Camilla, the role that she has with King Charles.”
When it comes to his eldest son, Prince Christian, it is unclear how his role will change when he becomes crown prince.
Rønde added: “I’m really excited about the role of his son, Prince Christian, because the Royal household said he will not have an official role until he turns 21, because they want him to focus on his education and just to be young.”
Queen of Denmark apologises for stripping grandchildren of royal titles
Queen Margrethe’s reign in pictures
What kind of king will he be?
Although the monarch is head of state, the Danish constitution strictly rules out their involvement in party politics.
But ever since climate conference COP15 took place in Copenhagen in 2009, the crown prince has been engaged with global climate and environmental challenges.
Ms Rønde believes the crown prince will be a “king of the people” when he officially becomes Frederik X.
“He meets a lot of Danes when he’s out and about and he’s very good at talking to them,” she said.
“[Queen Margrethe] is also a queen of the people, people really like her, but I think he will be too.”