blow someone's cover

blow (one's) cover

To expose one's true identity or motives after they had been intentionally concealed (i.e. after one had been "undercover"). The spy fled when he realized that someone had blown his cover. I totally blew my cover when I stupidly wore my school jacket to steal the other team's mascot.
See also: blow, cover

blow someone's cover

INFORMAL
If you blow someone's cover you tell other people who they are or what they are doing, when they are trying to keep it secret. Asking those kind of questions could blow my cover. The young man looked embarrassed, as if he were a spy whose cover had been blown.
See also: blow, cover

blow someone's cover

discover or expose someone's real identity.
See also: blow, cover
References in periodicals archive ?
It is not polite to blow someone's cover, especially when that someone is a lady, nay, a veritable grande dame.