Once-great king of magical city rumoured to be returning after many struggles (10)
I believe the answer is:
ozymandias
'once-great king' is the definition.
I know nothing about this answer so I can't judge whether this works.
'magical city rumoured to be returning after many struggles' is the wordplay.
'magical city' becomes 'Oz' (as in The Wizard of Oz).
'rumoured' becomes 'said' (said to be can mean rumoured to be).
'to be returning' shows that the letters should be reversed in order.
'after' means one lot of letters go next to another.
'struggles' is an anagram indicator.
'said' back-to-front is 'dias'.
'many' is an anagram of 'yman'.
'dias' put after 'yman' is 'ymandias'.
'oz'+'ymandias'='OZYMANDIAS'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for ozymandias that I've seen before include "Old king" , "Shelley's "king of kings"" , "Egyptian king" , "My name is -, king of kings (Shelley)" , "Shelley 24" .)