Preheat oven to 350 degrees. Line a 9x13 baking dish with parchment paper, set aside.
In a large bowl, prepare brownie mix according to manufacturer's instructions. Spread into the bottom of the 9x13 pan in a smooth, even layer. Set aside.
In another large bowl, combine red velvet cake mix, vegetable oil, egg and milk and mix until completely incorporated and smooth. Spoon onto brownie layer randomly and swirl very gently with a butter knife in different directions. I like to zig zag side to side then up and down. Bake for 20-22 minutes or until a toothpick comes out almost clean with a small amount of batter on it. This will ensure that your brownies will be fudgy. Allow brownies to cool completely before cutting into them.
Red Velvet Swirl Brownies will stay fresh for up to 3 days stored in an airtight container at room temperature.