Now, surprisingly, son appearing in court comes clean (4,2)
I believe the answer is:
owns up
'comes clean' is the definition.
(I've seen this in another clue)
'now surprisingly son appearing in court' is the wordplay.
'surprisingly' is an anagram indicator (a surprising ordering of the letters).
'son' becomes 's' (genealogical abbreviation for son).
'appearing in court' becomes 'up' (I've seen this in other clues).
'now' with letters rearranged gives 'own'.
'own'+'s'+'up'='OWNS UP'
(Other definitions for owns up that I've seen before include "Confesses, admits guilt" , "Admits (to something)" , "Admits responsibility" , "Allows" , "'Admits, confesses (4,2)'" .)