The operation the Duke of Edinburgh will undergo on Wednesday will require a general anaesthetic.
Buckingham Palace have not given any further details of the procedure, other than to say the operation is on his hip.
Most surgeons suspect the Duke is having a hip replacement operation – which is quite common for people of his age.
The Queen Mother had one of her hips replaced when she was older than her son-in-law.
She fully recovered from the operation at the age of 98, but that procedure was carried out after she broke her hip.
Wednesday’s elective surgery was planned as the Duke has been suffering from pain with his hip for the last month or so.
The Duke of Edinburgh had held that position until his retirement last year.
The Queen Mother spent nearly three weeks in hospital after her first hip replacement operation in 1995.