Brother to Remus (7)
I believe the answer is:
romulus
'brother to remus' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for romulus that I've seen before include "Fratricide" , "A founder twin of Rome" , "Brother of 25 across" , "Twin brother of Remus" , "Twin founder of city" .)