Diet Coke was introduced to the market in 1983, becoming the company’s first sugar free soft cola. Coca-Cola Zero then came out in 2006, before being phased out and replaced with Coca-Cola No Sugar. On the website, the brand explains the difference between the two beverages, and while they admit that both drinks are sugar free and calorie free, “Coca-Cola No Sugar looks and tastes more like Coca-Cola Classic, while Diet Coke has a different blend of flavours which gives it a lighter taste.”
Coke Zero contains the ingredients water, colour (caramel E150d), phosphoric acid, sweeteners (aspartame, acesulfame K), natural flavourings including caffeine, acidity regulator (sodium citrate). Meanwhile Diet Coke contains the ingredients carbonated water, colour (caramel E150d), sweeteners (aspartame, acesulfame K), natural flavourings including caffeine, phosphoric acid, citric acid.
It makes complete sense, especially for those who know the two products well and certainly goes a long way to explaining the flavour profiles of both beverages and why they differ so drastically.