After the fact

something that actually exists; reality; truth:
Your fears have no basis in fact.
something known to exist or to have happened:
Space travel is now a fact.
a truth known by actual experience or observation; something known to be true:
Scientists gather facts about plant growth.
something said to be true or supposed to have happened:
The facts given by the witness are highly questionable.
Law.. Often, facts. an actual or alleged event or circumstance, as distinguished from its legal effect or consequence.
Compare , .
after the fact, Law. after the commission of a crime:
an accessory after the fact.
before the fact, Law. prior to the commission of a crime:
an accessory before the fact.
in fact, actually; really; indeed:
In fact, it was a wonder that anyone survived.
noun
an event or thing known to have happened or existed
a truth verifiable from experience or observation
a piece of information: get me all the facts of this case
(law) (often pl) an actual event, happening, etc, as distinguished from its legal consequences. Questions of fact are decided by the jury, questions of law by the court or judge
(philosophy) a proposition that may be either true or false, as contrasted with an evaluative statement
(criminal law) after the fact, after the commission of the offence: an accessory after the fact
(criminal law) before the fact, before the commission of the offence
as a matter of fact, in fact, in point of fact, in reality or actuality
fact of life, an inescapable truth, esp an unpleasant one
the fact of the matter, the truth
n.

1530s, “action,” especially “evil deed,” from Latin factum “event, occurrence,” literally “thing done,” neuter past participle of facere “to do” (see factitious). Usual modern sense of “thing known to be true” appeared 1630s, from notion of “something that has actually occurred.” Facts of life “harsh realities” is from 1854; specific sense of “human sexual functions” first recorded 1913.
After an actual occurrence, particularly after a crime. For example, I know the brakes should have been repaired, but that doesn’t help much after the fact. The use of fact for a crime dates from the first half of the 1500s. The word became standard in British law and is still used in this way today. The idiom was first recorded in 1769 in the phrase accessories after the fact, referring to persons who assist a lawbreaker after a crime has been committed. Now it is also used more loosely, as in the example above.
In addition to the idiom beginning with
fact
also see:

after the fact
in fact
is that a fact
matter of fact