Father, royal, in favour of the sweet? That's what is expected (3,3,3,6)
I believe the answer is:
par for the course
'what is expected' is the definition.
I don't know anything about this answer so I cannot judge whether this works.
'father royal in favour of the sweet?' is the wordplay.
'father' becomes 'pa' (pa can mean dad or father).
'royal' becomes 'r' (common abbreviation e.g. RM - Royal Marine).
'in favour of' becomes 'for' (being for a particular cause).
'sweet?' becomes 'course' (sweet is a kind of course).
'pa'+'r'+'for'+'the'+'course'='PAR FOR THE COURSE'
'that's' is the link.
Can you help me to learn more?
(Other definitions for par for the course that I've seen before include "72?" , "achievement that seems full of holes?" , "Normal" , "Standard" , "Typical" .)