King Frederik will make his first trip outside Denmark since his accession, travelling to Poland from 31 January to 2 February.
While it was initially thought that his wife, Queen Mary, will act as regent for three days while Frederik is away for three days, the Danish royal palace has confirmed otherwise.
For the first time, Crown Prince Christian, 18, will assume the role of regent, the royal household has informed Danish magazine, Billed Bladet.
Duties can include signing laws, holding audiences and appointing and dismissing ministers.
Christian, who is in the final year of his secondary education at Ordrup Gymnasium in Gentofte, made a solemn declaration to abide by the Constitution at the Council of State meeting last November.
The declaration was a requirement for Christian to be able to be appointed regent in future, and now that time has come.
Queen Mary, Queen Margrethe's sister Princess Benedikte and Margrethe's youngest son, Prince Joachim, can all be acting regent and perform the duties of head of state.
For Christian, it's the latest in a long list of milestones of late. The prince turned 18 last October with his grandmother Queen Margrethe throwing him a lavish gala dinner in his honour.
© GettyTo mark the occasion, Margrethe also gifted Christian the Order of Elephant – Denmark's highest honour.
As Frederik became King on 14 January, Christian also took on a new royal title, becoming Crown Prince of Denmark.
© GettyIt was previously announced by the Danish royal palace that Prince Christian would not receive financial support from Folketing (Parliament) "until he turns 21 or upon a possible change of throne, if it takes place before that".
Given the change of throne, it's possible that Christian may be now receiving some of this royal allowance.
© GettyThe prince, who is the heir to the Danish throne, has three younger siblings – Princess Isabella, 16, and 13-year-old twins, Prince Vincent and Princess Josephine.
The young royals appeared on the balcony at Christiansborg Palace in Copenhagen shortly after their father Frederik was proclaimed King. Watch the moment below…
Queen Margrethe shocked the nation when she announced her decision to abdicate in her New Year's address.
She reigned for 52 years and will still be known as Her Majesty Queen Margrethe.
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