Preheat the oven to 425°F (220°C).

In a large mixing bowl, combine the sliced peaches, diced mango, sugar, cornstarch, cinnamon, and lemon juice. Stir gently until the fruit is well coated. Let the mixture sit for about 10 minutes to allow the juices to develop.

Roll out one pie crust and fit it into a 9-inch pie pan. Trim any excess crust hanging over the edges.

Pour the fruit mixture into the pie crust, spreading it evenly. Dot the top with small pieces of butter.

Roll out the second pie crust and place it over the fruit filling. Trim and crimp the edges to seal the pie. Cut a few slits in the top crust to allow steam to escape.

Brush the top crust with the beaten egg to give it a golden color when baked.

Bake in the preheated oven for 20 minutes. Reduce the temperature to 350°F (175°C) and continue baking for an additional 25-30 minutes, or until the crust is golden brown and the filling is bubbly.

Remove from the oven and let the pie cool for at least 2 hours before slicing to allow the filling to set.