Preheat the oven to 350 degrees.
Mix together cake mix, Dr. Pepper TEN and egg in a mixer on low until it's no longer dry. Don't over-mix.
Pour cake batter into cupcake wrappers (about 2/3 the way full).
Bake for 18-20 minutes. Let cool completely before frosting.
While cupcakes are baking, in another mixing bowl, add all ingredients for the filling. Mix until it's combined.
Once cupcakes are cooled, fill a piping bag with marshmallow cream mixture.
Place the piping tip (smaller sizes will work best) into each cupcake and fill them with the cream mixture.
Next, combine all frosting ingredients until it's completely smooth.
Pipe onto the cupcakes then serve!