The Duke of Edinburgh is spending his 92nd birthday in hospital as he continues to recuperate from an operation on his abdomen.
Buckingham Palace said Philip was "progressing satisfactorily" after undergoing the exploratory procedure at the London Clinic on Friday.
There will be two gun salutes in the capital to mark the Duke's birthday.
The first, a 41-round Royal Salute by The King's Troop Royal Horse Artillery, will take place in Green Park at noon, followed an hour later by a 62-round salute by the Honourable Artillery Company at the Tower of London.
Philip was admitted to hospital for the pre-arranged operation on Thursday, following a garden party at the Palace.
Prime Minister David Cameron took to Twitter to send a birthday message to the Duke.
Analysis of the results of tests on the Duke are expected to be completed this week, and he is likely to be in hospital for up to two weeks while he recovers.
Details of the original symptoms behind his admission have not been released, but it is thought the procedure did not involve his heart or bladder, organs the Duke has experienced problems with before.
The Queen spent the weekend at Windsor Castle, where she was updated with her husband's progress.