Board Thread:Metal Gear Solid V/@comment-5038094-20150615202500/@comment-3131736-20150616063137

Adachi Did It wrote: Has to be Solid surely, weren't he and Liquid the "Twin Snakes" doesn't make much sense for it to be Solidus. Saying that though, doesn't make much sense for it to be Solid either. Maybe a hallucination of some kind? MGSV trailers usually feature some kind of hallucination, so maybe? I have no idea what's going on :p but my hype levels just reached new heights.

I also think that it's either a hallucination or some other kind of trick pulled by Hideo. In MGS1, Solid does not know that he has a  twin until Liquid explains it to him prior to hijacking REX. Also, in the MGS1-briefing when Campbell hands Solid a picture of Liquid, Solid is seriously surprised and throughout the game, he mentions multiple times that he is not aware of having any twins.