I ______(tell) him the good news when I see him at the office.

I ______(tell) him the good news when I see him at the office.
I ______(tell) him the good news when I see him at the office.

I ______(tell) him the good news when I see him at the office.
I will tell (tell) him the good news when I see him at the office.
这是when引导的时间状语从句,要主将从现

will tell

will tell, 将来时
我看到他的时候， 会告诉他这个好消息的

will tell
时间状语从句，一般现在时表将来。