Prince Philip taken to hospital for surgery
The Duke of Edinburgh has been admitted to the London Clinic for an exploratory operation on his abdomen.
Philip is expected to remain at the London Clinic for up to two weeks.
The Palace said in a statement: "His Royal Highness The Duke of Edinburgh has been admitted to the London Clinic for an exploratory operation following abdominal investigations. He is expected to stay in hospital for up to two weeks.
"Further updates will be issued when appropriate."
Philip's admission to hospital was shortly after he attended a Buckingham Palace garden party this afternoon.
The Duke, who turns 92 on June 10, had missed an engagement at the palace on Monday night because he was feeling "under the weather".
Lord-Lieutenant of Nottinghamshire Sir John Peace attended today's garden party where he said Philip had been "telling jokes" - but he would not divulge what they were about.
Speaking of meeting the Queen at the event, he said: "It was wonderful to see the Duke of Edinburgh with her."
A Buckingham Palace spokeswoman said the planned admission came after this afternoon's garden party and added: "He is in very good health."
The operation will take place tomorrow, following the investigations that were carried out over the past week.
The Prince's illness earlier this week is not thought to be connected to tonight's admission to hospital.
She added: "He felt unwell on Monday and missed an engagement but that was down to the fact he had temporarily lost his voice."
The Queen will still perform her engagements as planned tomorrow, which include a visit to the new BBC studios in central London.
The Queen and Prince Philip had appeared together on the steps of Buckingham Palace at 4pm this afternoon, when the National Anthem was played to mark the start of the garden party.
Despite the fierce sun, with temperatures at approximately 22C (72F), the Duke appeared relaxed and happily chatted to guests as he walked around the garden, giving no indication of his imminent admission to hospital.
British Prime Minister David Cameron sent Philip his good wishes, writing on Twitter: "My best wishes to the Duke of Edinburgh who is in hospital tonight. I hope he has a swift recovery."