The 83-year-old queen, who took over the throne in 1972, is the longest-serving monarch in Europe following the death of Queen Elizabeth II in September 2022.
Archive photos show the young princess, then 31, stood at the balcony at Christiansborg Palace - just like her son did today - as the then-Prime Minister Jens Otto Krag proclaimed her monarch.
ROBERT HARDMAN: Barely a year into his reign, King Charles III will not be the new kid on the regal block for much longer. For we are about to bid farewell to the world s senior sovereign.