Preheat your oven to 350°F (175°C) and grease a standard loaf pan.
In a large mixing bowl, whisk together the brownie mix, eggs, water, and oil until smooth.
Scoop in the hot fudge and gently swirl it through the batter. Don’t overmix—it’s meant to be marbled.
Pour the batter into the loaf pan and smooth the top.
Bake for 50-55 minutes, or until a toothpick comes out mostly clean with a few fudgy crumbs.
Cool the bread in the pan for 10 minutes, then transfer to a wire rack. Drizzle more hot fudge over the top before serving.