Technically DS is an independent sibling of Citroën within Stellantis, a sprawling car conglomerate that owns a dog’s dinner of car brands in Europe and USA.
If we want to get really technical, “DS4” is a model from Citroën and they later spun out the DS lineup into its separate brand, with the “Citroën DS4” becoming “DS 4”, “DS” being the make and “4” being the model.