CNN: Atlanta, Georgia (CNN) -- Canadian authorities are investigating an "unbelievable" incident in which a passenger boarded an Air Canada flight disguised as an elderly man, according to a confidential alert obtained by CNN.

The incident occurred on October 29 on Air Canada flight AC018 to Vancouver originating in Hong Kong. An intelligence alert from the Canada Border Services Agency describes the incident as an "unbelievable case of concealment."

"Information was received from Air Canada Corporate Security regarding a possible imposter on a flight originating from Hong Kong," the alert says. "The passenger in question was observed at the beginning of the flight to be an elderly Caucasian male who appeared to have young looking hands. During the flight the subject attended the washroom and emerged an Asian looking male that appeared to be in his early 20s."