Queen embracing old flame in outbuilding (6)
I believe the answer is:
annexe
'outbuilding' is the definition.
(I've seen this before)
'queen embracing old flame' is the wordplay.
'queen' becomes 'anne' (Queen Anne, 18th-century queen).
'embracing' means one lot of letters goes inside another.
'old flame' becomes 'ex' (an ex-lover).
'anne' enclosing 'ex' is 'ANNEXE'.
'in' acts as a link.
(Other definitions for annexe that I've seen before include "Added section of document" , "Wing of the main building" , "Small building added to another" , "Supplementary attached building" , "Joined-on building" .)