The Singapore Sling was originally served at Long Bar in the Raffles hotel in Singapore around the turn of the century. The original recipe is attributed to Raffles bartender Ngiam Tong Boon and is a variant on the Gin Sling.
Our recipe evokes the classic recipe, which is fruit-forward, herbaceous and strong, though most incarnations of the “classic” Singapore Sling are based on general notes and nostalgia. Later, more modern incarnations of the drink created an overly sweet drink based more on grenadine than citrus. The earliest published version of the recipe was in the 1930 classic by Harry Craddock, “The Savoy Cocktail Book.” David A. Embury states in his book “The Fine Art of Mixing Drinks” that no two published recipes for the Singapore Sling are the same.

Reference : https://www.liquor.com/recipes/singapore-sling/