Crown Prince Frederik only learned of his mother Queen Margrethe's plans to abdicate just three days before her surprise announcement in her New Year's address.
A spokesperson from the royal palace confirmed to Danish newspaper Berlingske that the queen informed both her sons, Crown Prince Frederik and Prince Joachim, about her decision on 28 December.
Frederik will be proclaimed King from the balcony of Christiansborg Palace in Copenhagen on Sunday 14 January, following his mother's formal abdication at the Council of State.
From then he will be known as King Frederik X, while his wife Crown Princess Mary will become Queen.
Frederik was just three years old when Margrethe ascended the throne on 14 January 1972.
It will be the first time such an abdication has occurred in the Danish monarchy's history in nearly 900 years, the last being when Eric III Lam stepped down in 1146.
© GettyRoyal reporter Wim Dehandschutter previously told HELLO!: "I was very surprised by the announcement of her abdication. I interviewed Queen Margrethe in 2017 and I asked her about voluntary abdication, because we've had several in Europe, in the Netherlands, where it's tradition, and in my country, Belgium, and also in Spain.
"She gave the predictable answer at that time, she told me 'In this country, we haven't gone in for that way of handing over. It's always been you stay for as long as you live and that's the way I see it too.' At that moment, I didn't think it was a special answer because it was in line with expectations, it was believed that Margrethe would remain on the throne until her death."
© GettyIn her New Year's address, Margrethe alluded that one of the reasons for her decision to abdicate was down to health issues.
She said: "In February [2023] I underwent extensive back surgery. It went well, thanks to the skilled healthcare staff who took care of me. Of course, the operation also gave rise to thinking about the future - whether the time had come to leave the responsibility to the next generation."
While Prince Joachim will return to Denmark from the US for Crown Prince Frederik's accession, his wife, Princess Marie and their children, Count Henrik and Countess Athena, will not be travelling with him. The family currently reside in Washington D.C. where Joachim works as an attaché to the Ministry of Defence.
