And when what has been predicted occurs, for behold it is approaching, then they shall know that a prophet was among them."
And when this cometh to pass, (lo, it will come,) then shall they know that a prophet hath been among them.
When this comes to pass–for behold, it will come!–then shall they know, understand, and realize that a prophet has been among them.
And when this cometh to pass (behold, it cometh), then shall they know that a prophet hath been among them.
When this comes—and it is certainly coming—they will know that a prophet has been among them.