Poor man going after popular princess (8)
I believe the answer is:
indigent
'poor' is the definition.
(indigent means poor or needy)
'man going after popular princess' is the wordplay.
'man' becomes 'gent' (gent is a kind of man).
'going after' says to put letters next to each other.
'popular' becomes 'in' ('in' can mean trendy).
'princess' becomes 'di' (Princess Diana).
'in'+'di'='indi'
'gent' put after 'indi' is 'INDIGENT'.
(Other definitions for indigent that I've seen before include "Poor enough to need help from others" , "poor fellow" , "Badly off" , "Poor and needy" , "Impoverished, destitute" .)