Preheat oven to 350°F (175°C) and grease a 9x13-inch baking dish well so the cake does not stick.
Pour the peach pie filling into the dish, then add the drained sliced peaches. Spread the fruit evenly so every part of the dish has peaches.
Sprinkle the dry cake mix evenly over the peaches. Do not stir or mix. Make sure most of the fruit is covered.
Slowly pour the melted butter over the cake mix, moving across the dish to cover as much surface as possible.
Place the dish in the oven and bake for 40 to 45 minutes until the top is golden brown and the filling is bubbling around the edges.
Remove from the oven and let it cool for 10 to 15 minutes before serving so the texture sets properly. Serve warm.