Crossword Genius

Without notice, plans ambush in grand retinue (6-2-7)

Ross

I believe the answer is:

ladies-in-waiting

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

'without notice plans ambush in grand retinue' is the definition.
I can't judge whether this definition defines the answer.

'notice plans ambush in grand retinue' is the wordplay.
I cannot really understand how this works, but
'notice' could be 'ad' (both can mean an advertisement) and 'ad' is present in the answer.
'in' is present in the answer.
'grand' could be 'g' (synonyms) and 'g' is found within the answer.
This explanation may well be incorrect...

Can you help me to learn more?

(Another definition for ladies-in-waiting that I've seen is " Queen's attendants".)

I've seen this clue in The Times.
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