About fellow being a stand-in for the king (6)
I believe the answer is:
regent
'a stand-in for the king' is the definition.
I know that 'king' relates to this answer.
'about fellow' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'fellow' becomes 'gent' (synonyms).
're'+'gent'='REGENT'
'being' acts as a link.
Can you help me to learn more?
(Other definitions for regent that I've seen before include "One acting on behalf of an incapacitated monarch" , "Ruler appointed when monarch is too young or away" , "Closely; almost" , "Ruler in the absence of a monarch" , "Person appointed as acting monarch" .)