Diet Coke
Diet Coke does not use a modified form of the Coca-Cola recipe, but instead an entirely different formula. The controversial New Coke, introduced in 1985, used a version of the Diet Coke recipe that contained high fructose corn syrup and had a slightly different balance of ingredients. In 2004, Coca-Cola introduced Coca-Cola C2, which it claims tastes much closer to Coca-Cola but contains half the carbohydrates. In 2005, the company introduced Coca-Cola Zero (replaced by "Coca-Cola Zero Sugar" in 2017), a sugar-free variation of regular Coca-Cola.
New Coke
Finally, the Coca-Cola board decided that enough was enough, and plans were set in motion to bring back the old Coke. Company president Donald Keough revealed years later, in the documentary "The People vs. Coke" (2002), that they realized this was the only right thing to do when they visited a small restaurant in Monaco and the owner of the restaurant proudly said they had "the real thing, it's a real Coke," offering them a chilled 6 and 1/2 oz. glass bottle of original Coca-Cola.