Philip, the Duke of Edinburgh, was taken to hospital for the third time in eight months on Wednesday while he and the queen were staying at Balmoral, their Scottish royal residence. He was taken to Aberdeen Royal Infirmary.
"The Duke of Edinburgh is responding well to treatment. It is unclear when he'll be discharged but is likely to remain in hospital for a few more days," a palace spokesman said.
The George Cross Island Association wishes him a speedy recovery.