Mythic king who killed his father and married his mother (7)
I believe the answer is:
oedipus
'mythic king who killed his father and married his mother' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for oedipus that I've seen before include "person who married his mother" , "complex character" , "Legendary Greek king with mother complex" , "Mythical Greek king of Thebes" , "King of Thebes who married his mother" .)