The Duke of Edinburgh has been taken to hospital in Aberdeen by ambulance - the third time in eight months he's been hospitalised.
Sky News reports that the palace says it's a "precautionary measure".
Prince Philip was at Balmoral Castle with the Queen.
It's the third time the 91-year-old has ended up in hospital in the last eight months.
Daily Express royal correspondent Richard Palmer says Buckingham Palace is giving little away at the moment.
He says they're waiting for a full assessment from the experts at the Aberdeen Royal Infirmary before they release any further information about how serious this is.
The editor-in-chief of Majesty magazine, Ingrid Seward, says this is a clear message to the 91-year-old, to slow down.
She says it's really his age that's against him and the amount of work he does, and that she thinks he's probably physically and mentally exhausted.
Ingrid Seward says the operation he had at Christmas gave him more energy.
He says he's very much a doer and not a spectator, and this is his problem, he finds it very difficult to slow down.
The Royals had been touring on the Isle of Wight in the last few days.