Bucky
There might be another explanation for how he knows things. There was a guy here once from my world, but 5 years ahead of me. He knew me but I didn't know him. It was kinda creepy.
Nick told me he didn't have surgery, that's the face he was born with.
I doesn't make sense that Arva would let him in if he's with the bad people from your world. There are so many different worlds and different timelines represented here, there has to be another explanation.