Old Lore, I'm afraid. I can't find a resource for the originals I speak of here, so hopefully someone else will pitch in with some sauce for my retelling!
Twisted Fate was still born to Gypsies, which does kinda make sense for Bilgewater. His oldest lore assumes he was born to Serpentine Gypsies, as in the newest lore, but I couldn't find that for the lore just prior to it. Graves was found in the back of a Bilgewater bar as an infant, left with nothing but his swaddling blanket and a bottle of spiked milk. The two of them didn't meet each other until they were men, both grown up as con-men and cheaters in Bilgewater's Underground, in separate circles. It was the only way to survive: Men born with nothing risk everything, or die on the streets with nothing still. For them, it paid off. They cheated, gunned, gutted, and gambled their way to the very top of Bilgewater's underground networks until finally, after probably 20-somethin' years, the two men faced each other for their fortunes. It's said that people from all across Bilgewater gathered to watch them play...
There was no telling who would win. It could really go either way. Every card dealt seemed to shift the balance of play... Then, on the last hand, both of them flipped the same winning cards. While the crowd lost their minds with shock, joy, and anger, they both kicked back in their chairs, pondering each other. They were both the best at what they did, and now they knew it for sure. It was a partnership that would last a lifetime - or, so they thought.
That was allll before various Zaunite doctors got involved and turned them on each other. Hope you can find the source and read it for yourself!