Likely to happen, being terribly honest about character (2,3,5)
I believe the answer is:
on the cards
'likely to happen' is the definition.
(I've seen this before)
'terribly honest about character' is the wordplay.
'terribly' is an anagram indicator.
'about' is an insertion indicator.
'character' becomes 'card' (both can mean a humorous person).
'honest' is an anagram of 'onthes'.
'onthes' going around 'card' is 'ON THE CARDS'.
'being' acts as a link.
(Other definitions for on the cards that I've seen before include "A merry Christmas is" , "Quite likely" , "Likely to happen" , "to have a PAYE job?" , "place for 6 19 [SEASONALMESSAGES]" .)