Some in LA mourned this secret love affair (5)
I believe the answer is:
amour
'secret love affair' is the definition.
(I've seen this in another clue)
'some in la mourned this' is the wordplay.
'some in' indicates the answer is hidden within the clue.
'AMOUR' is hidden within 'la mourned this'.
(Other definitions for amour that I've seen before include "Love-affair" , "French lover" , "close relationship" , "Love affair, perhaps secret" , "beloved" .)