Preheat oven to 350 degrees (or 325 for a dark or non-stick pan).
Melt butter in the bottom of a 9×13 pan by placing in the warm oven for a couple of minutes.
Remove the pan from the oven & sprinkle in the brown sugar over the melted butter.
Place peach slices in your desired pattern in the bottom of the pan.
Top with drained pineapple. - Reserve the juice.
Add water to reserved pineapple juice to measure 3/4 cup.
Combine cake mix, juice mixture, oil & eggs in a large mixing bowl – mix on low 30 seconds.
Increase speed to medium & beat for 2 minutes.
Pour batter over the peaches & pineapple in the prepared baking dish & spread evenly.
Bake 45-55 minutes or until toothpick test comes out clean & the top is golden brown.
Remove from oven & immediately run a knife around the outer edges of the pan to loosen the cake.
Place a serving plate or cutting board upside down on top of the pan & then invert the pan & plate to release the cake.
Leave the pan over the cake for 1-2 minutes to allow all the toppings to drizzle back onto the cake.
Chill for at least 30 minutes before serving.
Keep covered & refrigerated until ready to enjoy.