The Duke of Edinburgh is spending a fourth night at Aberdeen Royal Infirmary in Scotland, where he is being treated for a bladder infection.
Prince Philip, 91, is understood to be responding well to a course of antibiotics.
Staying at nearby Balmoral, the Queen and the Royal family are in constant contact with the Duke and the doctors treating him.
This is the Duke's third hospital stay in recent months. He was admitted to hospital for five nights in June, missing several days of the Queen's Diamond Jubilee festivities.
It is not known if he will be healthy enough to attend the opening of the Paralympics in London on August 29.