know for a fact

To have definitive knowledge of something. I know for a fact that he cheats in cards! I saw the ace up his sleeve. My mom says she knows for a fact that I'm getting the internship at her company, but I won't believe it until the recruiter calls me.

See also: fact, for, know

See also:

for a fact
known fact
a fact of life
fact of life
facts of life
as it so happens
there's no help for (something)
there's no help for it
as it happens
fact

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