future tense

[jirikoo]

Hi to all,
once again a question about tenses, this time about future tense.

What other tense do we use after future tense?, for instance:

"I will let you know wheter I will come."

or is this sentence better?????:

"I will let you know wheter I come."

Basically, my question sounds if i can have two future tenses [one after another] in a clause.

thank you

[Tdol]

In your example, the second future is OK. Often after if/when/after/before we do use the present, though.