But was he telling the truth?
I don't suppose we'll ever know the truth about what happened that day.
To tell (you) the truth I'm quite pleased he's not coming.
To tell the truth, I don't enjoy shopping for clothes. (Preliminary English Test; B1; Farsi)
There may be some truth in what she says.
There is no truth in the reports of his resignation.
And yet what he says contains at least a grain of truth.
My humble opinion is that this statement is absolute, even though there is a great deal of truth behind it. (First Certificate in English; B2; Greek)
moral/religious truths
It was about those universal truths that one seeks all [one's] life and perhaps dies without truly understanding how happy one was. (Certificate of Proficiency in English; C2; Serbian)