One king guarding another that is less discreet (7)

'another that is less discreet' is the definition.
I can't tell whether this definition defines the answer.

'one king guarding' is the wordplay.
I cannot really understand how this works, but
'one' could be 'i' (Roman numeral) and 'i' is located in the answer.
'king' could be 'er' (abbreviation for Edward Rex, various English kings) and 'er' is found within the answer.
The remaining letters 'leak' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?