Crossword Genius

Titled French mistress who lost her head (2,5)

Ross

I believe the answer is:

du barry

I'm a little stuck... Click here to teach me more about this clue!

'titled french mistress who lost' is the definition.
I know nothing about this answer so I can't tell whether this works.

'her head' is the wordplay.
I cannot quite understand how this works, but
'her' could be 'barry' and 'barry' is located in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in the Evening Standard.
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