Well, the butter would certianly make it extra keto-friendly! lol
OTOH, I'll pass.
I used to like Diet Coke... my favorite was Diet Lime Coke, sadly discontinued some years ago. These days, however, Coke and the other name brands (diet or not) are too pricey at roughly TWICE the price they were but a few years ago, so I've forced myself to get used to the store brands.