It’s clear father came back by himself (8)
I believe the answer is:
apparent
'it's clear' is the definition.
('apparent' can be a synonym of 'clear')
'father came back by himself' is the wordplay.
'father' becomes 'pa' (pa is a kind of father).
'came back' shows that the letters should be reversed in order.
'by himself' becomes 'parent' (I can't justify this - if you can you should believe this answer much more).
'pa' in reverse letter order is 'ap'.
'ap'+'parent'='APPARENT'
Can you help me to learn more?
(Other definitions for apparent that I've seen before include "That may be seen" , "Seeming real or true" , "Visible - plain - presumable" , "Writ large" , "Obvious; seemingly true" .)