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I'll let you know where she lives.

--> As I know of, 'where she lives' is an object for 'know' in this sentence.

I'll let you know when she arrives.

-->But in this, 'when she lives' seems adverb. Then, can't it be understood as an object for 'know' like the 'where' clause in the first sentence?

If so, how can I express if I want to say 'I'll let you know the time when she arrives"?
Comments  
The verb is "let someone know."
To eliminate confusion:
I'll let you know that when she arrives.
I'll let you know the time when she arrives.

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I'll let you know as soon as she arrives.
I'll let you know the time of her arrival.
CJ
Students: We have free audio pronunciation exercises.
Marius Hancu
I'll let you know that when she arrives.

I'll let you know the time when she arrives.

Hi Marius Hancu,

What is 'that' referring to in the first sentence?

Thanks

PBF
Marius Hancu
I'll let you know that when she arrives.

I'll let you know the time when she arrives.

Hi Marius Hancu,

What is 'that' referring to in the first sentence?

Thanks

PBF
<> You may like a comma there:
<> I'll let you know that, when she arrives.
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Thanks for all of your answers.