I don't know how the concept of Twin Flames came into consciousness but it's a pretty widely known one in metaphysical/spiritual circles and has been referred to by that term since at least the early 1960s. If you went to Quora or just Googled Twin Flame you would find thousands of entries.
This story is based in both my own personal experiences as well as extensive reading on the topic. I didn't know about Twin Flames when I first met mine. We didn't understand what was going on for us until about 2 years into our relationship and then it suddenly all made sense because although there is some disagreement about some of the finer points, the general dynamic is the same for everyone. Realizing, "Oh, this is a thing. Now it all makes sense," was incredible.