Denmark’s Queen Margrethe II, Europe’s longest-reigning monarch, will abdicate on 14 January after 52 years on the throne and will be succeeded by her eldest son, Crown Prince Frederik, she announced on Sunday. The 83-year-old queen, who came to the throne in 1972, made the surprise announcement live on air during her traditional New Year’s Eve speech watched by many in the country of 5.9 million people.