Crossword Genius

In France, said to be a day boy? (3)

Ross

I believe the answer is:

des

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

'boy?' is the definition.

'in france said to be a day' is the wordplay.
I cannot quite see how this works, but
'day' could be 'd' and 'd' is found in the answer.
The remaining letters 'es' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for des that I've seen before include "and 9 Across: Former 'Countdown' host" , "- O'Connor, Br. singer" .)

I've seen this clue in the Evening Standard.
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