Fast Track and Dew XP

With spoilers and leaks abound I don’t want to use the search feature so forgive me if this has been brought up already but how will Fast Track and Dew XP work?
Will they stack? Or would it be pointless to use Fast Track if you have Dew matches left on your account?

Fast track is basically dbl xp so with the dew it would be 2 times more the xp, but only when u use it without fast track ud get normal amount of xp from the dbl xp u get