1.Boil sago in a large pot of water for 10 minutes; turn off heat, cover, and let sit for 10 minutes until translucent.
2.Drain sago and rinse under cold running water; set aside in a bowl of cold water.
3.Add one mango, coconut milk, evaporated milk, and sugar into a blender and blend until smooth.
4.In a medium bowl, combine the mango mixture with the drained sago and half of the pomelo. Mix well.
5.Cover and chill in the refrigerator for at least 1 hour. Serve chilled, topped with one diced mango and the remaining pomelo.