How is “truth will out” used?

In Harry Potter and the Order of the Phoenix (2007), one line is: “As the Muggles say, truth will out.”

Which movie is “truth will out” from?

The clip at the top of this page is from Harry Potter and the Order of the Phoenix (2007).

Idiom

used to say that people will find out the true facts about a situation even if you try to keep them secret

Heard in 14 movies

(the) truth will out
used to say that people will find out the true facts about a situation even if you try to keep them secret

Definitions from the Oxford Advanced Learner's Dictionary, 9th edition

As the Muggles say, truth will out.

Said in 8 films · #1