Posh boy advanced to embrace princess (2-2-2)
I believe the answer is:
la-di-da
'posh' is the definition.
(I've seen this before)
'boy advanced to embrace princess' is the wordplay.
'boy' becomes 'lad' (informal term for boy).
'advanced' becomes 'a' (abbreviation).
'to embrace' is an insertion indicator.
'princess' becomes 'di' (Princess Diana).
'lad'+'a'='lada'
'lada' going around 'di' is 'LA-DI-DA'.
(Other definitions for la-di-da that I've seen before include "Hoity-toity" , "Pretentious, snobbish" , "I'd a lad with affected manner or pronunciation" , "Stuck-up" , "Affectedly genteel" .)