Apparently ready for release of empire's supreme ruler (5)
I believe the answer is:
incan
'apparently ready for release' is the definition.
The definition suggests a singular noun which matches the answer.
'empire's supreme ruler' is the wordplay.
I cannot really see how this works, but
'ruler' could be 'inca' (I have seen 'Foreign ruler' mean 'inca' so perhaps 'ruler' could also mean 'inca') and 'inca' is present in the answer.
A single letter 'n' remains which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
'of' acts as a link.
Can you help me to learn more?
(Other definitions for incan that I've seen before include "From old Peru" , "like former Peruvian empire" , "associated with ancient culture" , "Relating to pre-conquest Peruvians" , "Relating to ancient South Americans" .)