Behold threesome featuring husband (Aylesbury's number one womaniser) (8)
I believe the answer is:
lothario
'womaniser' is the definition.
(Lothario is an example)
'behold threesome featuring husband aylesbury's number one' is the wordplay.
'behold' becomes 'lo'.
'threesome' becomes 'trio' (synonyms).
'featuring' is an insertion indicator.
'husband' becomes 'h'.
'aylesbury's number one' becomes 'a' (1st letter of 'aylesbury').
'h'+'a'='ha'
'trio' placed around 'ha' is 'thario'.
'lo'+'thario'='LOTHARIO'
(Other definitions for lothario that I've seen before include "A Gay libertine" , "Fictional seducer" , "Libertine - ol' hot air (anag)" , "Dissolute" , "A literary libertine or womaniser" .)