Board Thread:General Discussion/@comment-184.78.138.250-20130809050624/@comment-1.64.184.209-20130809074522

Okay without myself going back into the details of each story, here is a "brief" answer.

Solid knows not anything about Liquid until Shadow Moses' mission breifing. Near the end, Liquid confirmed to him that they were twins and the story had no elaborate further on whether he looked up his family history afterwards. In my memory, he already knew Solidus is George Sears when we play as Raiden in MGS2 and there's no mentioning of how he found this out.

As for Liquid, things are a bit complicated. It is clear that Liquid knows Solid is his "other half" long before MGS1, but there is no direct mentioning within MGS1 that he knows about Solidus. Solidus is first mentioned at the very very end of MGS1 by Ocelot (by the time which Liquid is already dead). Then it becomes a matter of who Liquid Ocelot in MGS2 really is - whether he is simply Ocelot pretending to be Liquid (as said in MGS4) or was he under the influence of Liquid's ghost. The latter has never been confirmed in-game except if you count the digital novels. If Liquid Ocelot is Ocelot himself all along, then the answer is simple, he knew about Solidus long ago (Solidus sent him to provoke Liquid to bring about the Shadow Moses incident). If Liquid's ghost is involved, then he probably knows about it when he dove into Ocelot's mind.