God only knows
No one knows (except for God). God only knows how long it will take for my application to be processed. A: "How do you think you did on your exam?" B: "God only knows!"
God only knows!
Inf. Only God knows.; No one knows but God. Tom: How long is all this going to take? Alice: God only knows! Bob: Where are we going to find one hundred thousand dollars? Mary: God only knows!