Crossword Genius

Boy! Saint-Laurent admits 50 old mistresses! (4-5)

Ross

I believe the answer is:

lady-loves

'mistresses' is the definition.
(female lovers)

'boy saint-laurent admits 50 old' is the wordplay.
'boy' becomes 'lad' (informal term for boy).
'saint laurent' becomes 'yves' (I've seen this in another clue).
'admits' is an insertion indicator.
'50 old' becomes 'lo' (I can't justify this - if you can you should give a lot more credence to this answer).
'yves' enclosing 'lo' is 'yloves'.
'lad'+'yloves'='LADY-LOVES'

I've seen this clue in The Independent.
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