Royal protection officers were said be "jittery" after a genuine intruder had been found in the Palace’s state rooms two days earlier....I've looked at the photo at the link, and I have to say, Prince Andrew looks like some guy. Would you recognize him outside of his natural habitat? Yes, he was in his own "gardens," but if he were unaccompanied and dressed nondescriptly, would you know it was him and not one of the "genuine intruders"?
[A] royal insider said: “Everyone is talking about these two incidents and can’t quite believe what has happened. The fact that this guy was able to wander off unchallenged and not be spotted by anyone is bad enough. But then to mistake the Duke for another intruder is almost incomprehensible. There is a high turnover of the police on duty at the Palace, but you’d think anyone would know what Prince Andrew looks like."
September 9, 2013
"Armed police pointed their guns at Prince Andrew and ordered him to 'put your hands up and get on the ground'..."
"... after mistaking him for an intruder in the gardens of Buckingham Palace."