That's honest to God truth

Hi ther,
Does anyone use "God truth" as in "truth"?

==It was like we became friends first, that's the honest to god truth"?

thank you

The crucial phrase is, I think, 'Honest to God', rather than 'God truth'. It is reasonably common I think, and derives, presumably, from the speaker asking God to validate the truth of the statement - swearing an oath, if you like:

'That is the truth, honest to God,' might be another way of saying it.

DFG