Crossword Genius

What reveals the calm lady on the summit is a princess? (3,6,8)

Ross

I believe the answer is:

her serene highness

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

'a princess?' is the definition.
Both the definition and answer are singular nouns.
Perhaps they are linked in a way I don't understand?

'what reveals the calm lady on the summit' is the wordplay.
I cannot really understand how this works, but
'what' could be 'eh' (sound used to ask 'what?' or 'pardon?') and 'eh' is found within the answer.
'lady' could be 'her' (I've seen this before) and 'her' is present in the answer.
'on' could be 're' ('on' can be mean 'with reference to') and 're' is located in the answer.
This explanation may well be incorrect...

'is' is the link.

Can you help me to learn more?

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