Caligula's nephew (4)
I believe the answer is:
nero
'caligula's nephew' 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 "Tyrannical Roman emperor" , "Roman emperor on the fiddle?" , "Ancient Roman emperor" , "Imperial Roman fiddler" , "Famous fiddler" .)