Strong emotion of father losing son (3)
I believe the answer is:
ire
'strong emotion' is the definition.
(I've seen this in another clue)
'father losing son' is the wordplay.
'father' becomes 'sire' (synonyms).
'losing' suggests deleting specific letters.
'son' becomes 's' (genealogical abbreviation for son).
'sire' with 's' taken out is 'IRE'.
'of' is the link.
(Other definitions for ire that I've seen before include "Anger among admirers" , "Displeasure" , "exasperation" , "Intense anger" , "Choler" .)