Prince Harry is to march on parade at Sandhurst military academy - but not in front of his grandmother, the Queen, as originally planned.
The Queen does not want to pass her cold on
Her planned presentation of Colours to the academy is one of three engagements cancelled after she caught a cold.
Harry, 20, will be among 700 officer cadets standing to attention in front of the Old College building.
Chief of the Defence Staff Sir Michael Walker will now present the Colours at the base in Camberley, Surrey.
The Queen, 79, has also had to cancel a reception for the Centenary of the Friends of the Elderly and an audience with the president of Singapore.
A Palace spokeswoman said: "It's no more than a bad cold."
The Queen's spokeswoman added: "The cold has affected her voice - she didn't want to pass on her cold to those she was meeting."
More than 3,500 members of cadets' families, friends and staff will gather to watch Tuesday's formal occasion.
Last week, a security review was launched after a newspaper reporter gained access to Sandhurst.
The Sun said its journalist walked in the grounds of the academy for seven hours after posing as a student.
Once inside, the reporter constructed a fake bomb in his car and took grainy video footage of a cadet the paper claimed was the prince.
Royal aides later said the cadet pictured looked like the prince but was not him.
Defence Secretary John Reid ordered a "quick investigation" into what he termed a "serious security breach".
- Prince William was expected to celebrate his 23rd birthday in private on Tuesday.