when you will come, when you come

[joham]

As soon as he comes back, I'll tell him when you ____ and see you.
The given answer is 'will come'. I was wondering if we could also use 'come', since if there is already a future tense in the main clause, we tend to use the present tense instead of the future tense in the subordinate clause.
Might I ask native English teachers to help me with this question? Thank you very much.

 

[Mohammed Abu Risha]

Joham

Conisder the following sentences:

I will tell you when they come.
I will tell you when they will come.

"When they come" in the first sentence is an adverbial of time. The sentence therefore means that: You are waiting for some people to come. Immediately after they come, you will pick up the phone and tell him.

The second sentence is different. "When they will come" is a nominal clause functioning as the object of the verb "tell". Here it means that you will tell your friend the time they will come. Let us assume for instance that they will come at 3. Then, the sentence means that you will tell him that "they will come at 3".