"Carbuncles!" Prince finally agreed - "they're monstrous, not good" (8)
I believe the answer is:
eyesores
'carbuncles' is the definition.
(I've seen this before)
'prince finally agreed they're monstrous not good' is the wordplay.
'prince finally' becomes 'e' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'agreed' becomes 'yes' ('agreed' can mean 'yes').
'they're monstrous' becomes 'ogres' (I've seen this in another clue).
'not' suggests deleting specific letters.
'good' becomes 'g' (abbreviation).
'ogres' with 'g' taken away is 'ores'.
'e'+'yes'+'ores'='EYESORES'
Can you help me to learn more?
(Other definitions for eyesores that I've seen before include "Carbuncles" , "views people find offensive" , "ugly looking things" , "They are offensive to see" , "unattractive prospects" .)