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
Farlex Dictionary of Idioms.

blow someone’s cover

tv. to reveal someone’s true identity; to ruin someone’s scheme for concealment. The dog recognized me and blew my cover.
See also: blow, cover
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions
See also:
  • blow (one's) cover
  • blow cover
  • blow one's cover
  • blow somebody's cover
  • blow someone's cover
  • snipe at
  • snipe at (someone or something)
  • throw a game
  • certain party
  • dead weight