Organ, as it happens, last of tour (5)
I believe the answer is:
liver
'organ' is the definition.
(liver is a kind of organ)
'as it happens last of tour' is the wordplay.
'as it happens' becomes 'live' (as in live television).
'last of' suggests the final letters.
The last letter of 'tour' is 'r'.
'live'+'r'='LIVER'
(Other definitions for liver that I've seen before include "Vital organ" , "Part of body" , "Bile-secreting gland" , "Dark reddish brown" , "Human organ" .)