So… why a controller?
just use a bone transform.
You need to drive its Alpha value some way or another.
I suggest you add a curve to the animation in use where the bone is animated.
a Metadata of 1 should suffice.
To hook it up, in animBP just create a float, set it to 1 by default. Use it to power the alpha on the bone node.
You can pull the curve info - and multipy by -1 to reverse it then subtract from the variable before pluggin in.
The idea is that a value of 1 in the curve will NOT apply the transform. While 0 or no value at all will.