With this, paradoxically, only slim hope? (3,6)
I believe the answer is:
If this is the answer, I'm afraid I cannot explain it.
Can you help me to learn more?
(Other definitions for fat chance that I've seen before include "that won't happen" , "Slim hope, paradoxically!" , "It will never happen!" , "No likelihood at all!" , "Slender hope (odd though that sounds)" .)