The Duke of Edinburgh will remain in hospital for a second night after becoming ill late on Tuesday, Buckingham Palace has said.
Prince Philip was admitted to hospital with an infection last night but it was understood be a precautionary measure a rather than an emergency.
There is usually a doctor on hand when the Queen and Duke are in residence at Windsor, as they were last night after spending the afternoon at Ascot.
The Duke did not need to be rushed to the nearest hospital to Windsor, instead opting for the King Edward VII in central London.
Buckingham Palace are not giving details of his illness but we know it is connected to one of his previous infections - he's had bladder infections before.
A spokesman said on Wednesday evening: "The Duke of Edinburgh continues to be in good spirits and will stay in hospital overnight tonight."
But he has also expressed his disappointment at not being able to attend the State Opening of Parliament and a second day at Royal Ascot.
As for when he might be discharged, there is a hands it could happen later today bt he may also be kept in for checks for a second night.
At the moment, and unless things change, the Queen is not planning to visit her husband.
The Duke was at the Queen's side on Tuesday for the opening day of Royal Ascot and seemed in good spirits.
He has enjoyed good health throughout much of his life, recovering from a blocked coronary artery in 2011 and a bladder infection in 2012, the latter leading him to miss the majority of the Queen's Diamond Jubilee celebrations.
His decision to retire from public duties after the summer was not health-related, Buckingham Palace said at the time of the announcement earlier this year.
The Duke is an advocate of healthy eating combined with exercise. He once said he more or less followed the Atkins diet and he drinks only moderately.
He takes the stairs rather than lifts and still fits into the uniform he wore on his wedding day.
He is well-known for his robust constitution. He told a flu expert at a research centre last year that he had not had the illness for 40 years.