(idiomatic,informal)Used to positively assert the frank honesty of an associated statement of set of statements; equivalent to "to you tell the truth".
1994,Lawrence Block,A Long Line of Dead Men:
"What's the point? Your buddies can kick back and relax. I'm going into voluntary retirement." / "Oh?" / "Tell you the truth, I was getting a little tired of Jim Shorter. Tired of that little room on Ninety-fourth Street. You know what I might do? I might leave town."
Usage notes
Used bracketed by punctuation, especially commas, dashes, or parentheses.