What I don't get is why Obi Wan would say: "that boy was our last hope"
Yoda said: "no, there is another"
You'd think since he took Padme from Mustafar to Polis Massa and witnessed the birth of the twins and then agreed to separate them that he would have known "there is another". Something he seems to know all about in Return of the Jedi. When I saw the originals, a long long time ago, I always assumed that Yoda had told him on Degobah after the "no, there is another" and that's how Obi Wan found out. With the prequels it made him look...absent minded.
Or sexist...