FBI agent, good fellow (1-3)

I believe the answer is:

g-man

'fbi agent' is the definition.
(I've seen this before)

'good fellow' is the wordplay.
'good' becomes 'g' (abbreviation).
'fellow' becomes 'man' (fellow can mean a man).
'g'+'man'='G-MAN'

(Other definitions for g-man that I've seen before include "Officer of the FBI in USA" , "FBI agent" .)

I've seen this clue in The Telegraph.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.