Adopted son of Claudius (4)
I believe the answer is:
nero
'adopted son of claudius' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for nero that I've seen before include "Roman arsonist and fiddler" , "Emperor (who fiddled while Rome burned?) d. AD68" , "Roman Emperor, 54-68 AD" , "Matricidal emperor" , "Fiddling Roman emperor" .)