Fruit old, as it happens (5)
I believe the answer is:
olive
'fruit' is the definition.
(I've seen this before)
'old as it happens' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'as it happens' becomes 'live' (as in live television).
'o'+'live'='OLIVE'
(Other definitions for olive that I've seen before include "Small green Mediterranean tree fruit, nice in martini" , "One's stoned" , "This branch is offered in peace gesture" , "Oil-producing fruit" , "girl" .)