Blow (one's) cover informal verb phrase
If you "blow one's cover", you intentionally cause one's secret information or nature exposed.
David was fired because he had made a bad mistake that blew his company's cover.
Everyone had thought she was a nice girl until her scandal blew her cover.
His cover was blown when he was caught having an affair with another girl.
The verb "blow" should be conjugated according to its tense.
This expression uses "blow" in the sense of “expose or betray,” a usage dating from Shakespeare's day.