The brand is also being given a packaging revamp with 'foil fresh' wrappers that replicate the popular old-style foil packaging, dropped in 2002.
Kit Kat Dark, which is launching on 18 September backed by a £1m marketing campaign, is targeting a major consumer trend towards plain chocolate. Nestlé said its research showed that more than half of 35 to 45-year-olds eat dark chocolate and that 39% of consumers would like to see a dark Kit Kat.
Dark is the latest in a long line of launches for the brand. In the past two years, four-finger innovations have included Lemon Yoghurt, Luscious Lime, Blood Orange, White and Caramac, all of which have experienced varying degrees of success. Most have subsequently been dropped, but Nestlé Rowntree promised that Dark was here to stay.
Sales communications manager Graham Walker said: "We not only expect to bring new consumers into the Kit Kat brand, but also more consumers into the already growing dark chocolate market."
The launch marks an increasing shift towards dark chocolate by the major confectionery players, and follows in the footsteps of brands such as Green & Black's. Cadbury is said to be launching a dark chocolate variant of its Flake.
Nestlé Rowntree already produces a dark chocolate two-finger biscuit in multipacks, but said the new entrant was unique to its four-finger line in the UK. The bar is made from higher quality chocolate than the two-finger variant and has a 52% cocoa solids content. It carries a premium price tag of 39p, a 4p increase on the standard milk Kit Kat, and will be aimed at an older demographic.
The packaging revamp, also launching in September across dark and milk four-finger lines, coincides with a new recipe for Kit Kat four-finger milk, which will contain more chocolate for an improved taste. It will backed by a £5m marketing campaign.