Explaining how the siblings came to design the product, Slovakian David told The Evening Standard: “We are heavy coffee drinkers. Like many other people we struggled with the teeth stains caused by it. There was nothing on the market that would suit our needs so we decided to create our own recipe.”

They spent three months perfecting the recipe, which, despite appearances, is most definitely coffee.

However they have been sure to keep it a closely guarded secret: the only clues they will reveal is that CLR CFF is produced using freshly roasted Arabica beans, and it contains zero preservatives, stabilisers or sweeteners.

Someone's invented a clear coffee that won't stain your teeth