Greek sun god, son of Zeus (6)
I believe the answer is:
apollo
I believe this is a double definition.
'greek sun god' is the first definition.
(I've seen this before)
'son of zeus' is the second definition.
(I've seen this before)
(Other definitions for apollo that I've seen before include "Handsome young man of Greek mythology" , "US spacecraft" , "Greek god of light, son of Zeus" , "US space project, 1960-72" , "handsome youth" .)