Forgive former partner’s hint about son (6)
I believe the answer is:
excuse
'forgive' is the definition.
(excusing is a kind of forgiving)
'former partner's hint about son' is the wordplay.
'former partner' becomes 'ex' (an ex-partner).
'hint' becomes 'cue' (cue can mean a hint or prompt).
'about' means one lot of letters goes inside another.
'son' becomes 's' (genealogical abbreviation for son).
'cue' placed around 's' is 'cuse'.
'ex'+'cuse'='EXCUSE'
(Other definitions for excuse that I've seen before include "Grant exemption or release to" , "Make allowances for; forgive" , "A defence for bad behaviour" , "Let off; defence" , "Let off the hook" .)