The Revelation of Star Wars V

So, Star Wars V: The Empire Strikes Back, was on spike this weekend... And it dawned on me. There is the line between Yoda and Obi-Wan on Degobah, and it goes something like this (off the top of my head)

Obi-wan

"that boy was our last hope."

Yoda

"no, There is another."

Who was Yoda talking about? Now, your/my/everyones first response will be, "Leia!". But I tell you now, that response is wrong. Sure when the original trilogy came out that response would be full filled with the announcement of Leia being Luke's sister in the next movie Revenge Return of the Jedi.

But, now that the prequel trilogy has been made and is now apart of Star Wars lor (not mentioning if they were good or not). Now after reviewing Return on the jedi we see a little bit more into the character of Obi-Wan. Without the prequel we know that Obi-Wan knew about Leia. He knew that she was the daughter of Skywalker. So that being, why would he place all hope in Luke and none in Leia who, he knew was still alive. So the other, who is it?

I feel that this is a very open ended string...

I dont know what are your thoughts?