Octavia's spouse (4)
I believe the answer is:
nero
'octavia's spouse' 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 Emperor, 54-68 AD" , "Tyrannical Roman emperor" , "Ancient Roman emperor" , "Roman 9" , "Roman emperor on the fiddle?" .)