Frank's about to follow after (7)
I believe the answer is:
sincere
'frank's' is the definition.
(frank can mean sincere or honest)
'about to follow after' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'to follow' says to put letters next to each other.
'after' becomes 'since' (I've seen this in another clue).
're' after 'since' is 'SINCERE'.
(Other definitions for sincere that I've seen before include "'Genuine, not deceitful (7)'" , "Open and genuine, not deceitful" , "Unfeigned, genuine" , "Perfect" , "Free from pretence" .)