Frederik is now set to become head of state of Denmark, Queen Mary and their eldest son Christian, 18, crown prince, after Margaret signed abdication papers at a Council of State meeting inside Christiansborg Palace, the seat of the Danish parliament.
Abdication would leave Denmark with two queens while Margaret would retain her title.
King Frederik, 55, is then scheduled to make his first public appearance on the balcony alongside the Danish Prime Minister who was due to officially announce him as the country's new regent. Crowds also hope to see Mary appear on the balcony. The couple married in 2004 and now have four children.
Her sister, Jane Stevens, who lives in Hobart, traveled to Copenhagen for the occasion.
The new king and queen are due to leave Christiansborg Palace in a horse-drawn carriage and return to the royal residence, Amalienborg, where Margaret also lives but in a separate building. The royal standard would be lowered in Margaret's house and raised in the building where Frederick and Mary lived.
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Four guns in Copenhagen Harbor will fire a 27-3 gun salute. In the late afternoon, Copenhagen's Tivoli Gardens amusement park plans to celebrate the new king and queen with the largest fireworks display in the park's 180-year history.
Across town, Australian expatriates registered on the Australian Embassy's email database known as the 'Vegemite List' were invited to join Ambassador Kiren Ayyalaraju for an evening to celebrate Mary's promotion.
Prime Minister Anthony Albanese announced over the weekend that the Federal Government will make a $10,000 donation in Mary's honor to Wildcare Tasmania to support its efforts to ensure the survival of the Tasmanian devil.
The gesture follows the Tasmanian gift of a handcrafted Huon Pine occasional table to Mary and Frederick.
“The story of Crown Prince Frederik and Crown Princess Mary of Denmark is one that Australians have followed closely and hold close to their hearts,” Albanese said.
“Crown Princess Mary grew up in Tasmania, so it is fitting that Australia marks the occasion with a gift to support Tasmanian devil conservation.
The City of Hobart is marking the occasion by planting a blue gum tree in a prominent location.