Truest

(of a statement) Conforming to the actual state of reality or fact; factually correct.

"This is a true story."

Conforming to a rule or pattern; exact; accurate.

"a true copy;   a true likeness of the original"

Of the state in Boolean logic that indicates an affirmative or positive result.

""A and B" is true if and only if "A" is true and "B" is true."

Loyal, faithful.

"He’s turned out to be a true friend."