A diamond ring turned up in the end? (5)
I believe the answer is:
'the end?' is the definition.
'a diamond ring turned up' is the wordplay.
'diamond' becomes 'gem' (I've seen this in other clues).
'ring' becomes 'o'.
'turned up' is a reversal indicator.
'agemo' written backwards gives 'OMEGA'.
'in' is the link.
(Other definitions for omega that I've seen before include "Traditional story" , "Ending of a series or sequence" , "Last thing" , "completes a series" , "Greek long 'o'" .)