Denmark’s Queen Margrethe II, whose half-century reign makes her Europe’s longest-serving monarch, has undergone “extensive back surgery” and the condition of the monarch “is good and stable under the circumstances”, the palace said.

The 82-year-old queen will remain in hospital “for some time to come”, and that will be followed by a period of convalescence and rehabilitation, according to the royal household.

Several official engagements have either been postponed, cancelled or are being handled by other members of the royal family.

The queen’s oldest son, heir to the throne Crown Prince Frederik, and his wife Crown Princess Mary will step in, as well as the queen’s sister Princess Benedikte, the palace said on Wednesday hours after the surgery.