G'day, I've had this problem latly that has been driving me crazy, any help on what to do would be appreciated.

basicly i've been given a cube with the top like this (the slopy drawring attached) and i've been told the 3D coordinates of A and C. What is the best method of calculating points D and B with the only other information given is that we're talking about a pefect cube placed on a slant, so only the Z coordinates of B and D are the same.

I have calculated the vector between A and C, and also the midpoint of the line (also the midpoint between D and B) however i now have no idea how to proceed.

ANY help appreciated greatly.