Beloved chain-smoking octogenarian monarch Margrethe II made a bombshell New Year's Eve announcement that she would be the first Danish royal to abdicate the throne in 900 years.
The royal couple are set to bring generational change to the Danish throne, more than 23 years after their modern fairy tale started in a Sydney pub during the 2000 Olympics.
Tens of thousands of people are braving Copenhagen's 3C (which feels like -1 including the wind chill factor) to catch a glimpse of the new monarchs.
The pair arrived at the parliament Christiansborg by car while the retiring regent, who is well known for her ballet costume design and archaeology hobbies, travelled in an 1891 black-lacquered mahogany horse-drawn coach.
Frederik, 55, becomes Denmark's head of state, Mary, 51, will be Queen and their eldest son 18-year-old Christian the Crown Prince, the moment Margrethe signs abdication papers at a state council meeting.
Among the sea of red and white Danish flags are some blue ensigns with the Southern Cross - a nod to Mary's homeland.
Frederik and Mary met in Sydney during the 2000 Olympics. (AP PHOTO)
Mary's Hobart-based sister, Jane Stephens, has travelled to Copenhagen.
Across the harbour, military personnel will fire cannons in a three-by-27-shot honorary salute to mark the royal handover.
Brisbane biomedical science graduate Ebony Wilson, 25, and her grandmother Judy bought a last-minute plane ticket to Copenhagen on Wednesday to be part of the historic moment.
''I was thinking about it and then I thought, why not be spontaneous? It's a once-in-a-lifetime opportunity,'' she told AAP in Copenhagen.
Brisbane graduate Ebony Wilson and her grandmother Judy travelled to Copenhagen for the succession. (Lisa Martin/AAP PHOTOS)
Royal enthusiast Rene Jensen 33, from Copenhagen, donned a plastic crown and a red cape over his winter jacket.
''I think (Mary and Frederik) are a powerful couple,'' he told AAP.
The Danish royal succession is set to be a low-key affair, with the main event about 1am (AEDT) when most Australians will be sleeping.
King Frederik is scheduled to make his first public appearance on a balcony alongside the Danish prime minister who will formally proclaim him as the country's new regent.
The public hopes to also see Mary appear on the balcony.
Mary's elevation to Queen comes 23 years after she met the Danish Crown Prince in a Sydney pub during the 2000 Olympics.
Mary and Frederik married in May 2004 and have four children.
Crowds are gathering in Copenhagen's Christiansborg Castle square ahead of the Queen's abdication. (AP PHOTO)
Aussie expats on the Australian embassy's email database known affectionately as the ''Vegemite List'' are joining ambassador Kerin Ayyalaraju for a soiree to toast Mary's promotion.
''I hope more Danes will be inspired to visit Australia to see where their new Queen was born and raised,'' Ms Ayyalaraju said.
The royal handover has generated a major tourism boost to the capital with a surge in hotel and rail bookings, according to tourism body Wonderful Copenhagen.
In Australia, events are planned at Sydney's Slip Inn where the two first met, and in Mary's home state of Tasmania, where landmarks will be lit in Denmark's red and white colours.
Opposition Leader Peter Dutton said Australians were proud the nation would have its own queen.
"Princess Mary is somebody who has been for a long period of time capturing the hearts of people around the world," he said.
