As you might have heard, Samsung makes some components for iPhones. Samsung is the only company that can make OLED displays, NAND flash, and DRAM chips in the quantities Apple needs for their phones.
Samsung expects to make $110 per each iPhone X sold, be offering these components to them. With the current sales estimates, this could lead to $4 billion more in revenue for the conglomerate than they would make with the sales of their Galaxy S8 phones. Samsung's manufacturing arm accounts for 35% of the corporation's revenue.
That is how the two fiersest competitors in the smartphone industry depend on each other, folks.