Looking on the internet deeply has found these results:

I will let you know when I'm going to be free is the most popular phrase on the web.

I will let you know when I will be free 11 results on the web	I will let you know when I'm going to be free 1800,000,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
And I will let you know when I'm ready to look at them. I will let you know when a good time is. I promise. But I will let you know when you cracked the case. I will let you know when it is finished. I will let you know when and how I will collect him. And when I have curried favor with her, I will let you know. I will let you know when I'm joking. Well, I will let you know when the king is back.	I want to let you know I'm going to go on record, I'm just calling to let you know I'm going to have a lie down. fashioned cause I believe the name on the outside of a place ought to let you know what's going on in the inside. And I will let you know when I'm ready to look at them. I just wanted to apologize on behalf of truck 81 for your missing item, and to let you know we're going to get to the bottom of it. I'm old I will let him know you're going to call. I will let you know when I'm joking.

I will let you know when I will be free

11 results on the web

I will let you know when I'm going to be free

1800,000,000 results on the web

More popular!

I want to let you know I'm going to go on record,
I'm just calling to let you know I'm going to have a lie down.
fashioned cause I believe the name on the outside of a place ought to let you know what's going on in the inside.
And I will let you know when I'm ready to look at them.
I just wanted to apologize on behalf of truck 81 for your missing item, and to let you know we're going to get to the bottom of it.
I'm old
I will let him know you're going to call.
I will let you know when I'm joking.