Fake Royal Guard?

An American person claims that a Royal Guard spoke to her outside one of the royal palaces (I think it was Buckingham Palace) when he realized nobody was around, and told her he was not a real soldier. I don't find this story plausible, but is there any definitive way of proving it?
Asked Jul 19, 2014

TIP: If it's not your answer to this question, please click "Leave a Comment" button under the question to communicate with the question owner.