The difference between the meanings of two sentences

Question

1) I will tell you when he comes.

and

2) I will tell you when he will come.

Is the difference between the two sentences (apart having different tenses) the answer, one the first does not need any answer more a kind of info but second is a question and need a precise answer

Answer 1

I will tell you when he comes, usually means that I will inform you when he has actually arrived. Comes in this case almost always means arrives.

I will tell you when he will come usually means that, before he actually arrives, I will tell you when he intends to come.

Neither sentence calls for an answer, since they are not posed as questions.

Answer 2

I will tell you when he comes.

• Means that you will send a notification upon his (the person you're expecting to arrive) arrival.

I will tell you when he will come.

• Means that you will send the information in relation to the time (schedule, in general) of his (the person you're expecting to arrive) arrival.

Note that the word 'when' here was not used in an interrogative fashion. You may refer here.

Answer 3

I think "I will tell you when he comes" is grammatically correct. "when he comes" is an adverb clause of time and in the adverbial clause of time we use present tense but it gives future meaning. It is also correct in cases of other adverb clauses of time. For example:

I will go as soon as he comes. If it rains, I will not go.

https://www.englishgrammar.org/adverb-clause-time/