sonofjones said:

yeah but if R2 is in the prequels it should at least be more than coincidence he's in the prequels and happens to end up in Leia's hands. For example, since C-3PO is being made Padme's droid, it can easily be assumed, once Leia is revealed as Padme's daughter, that Leia inherited him after her mother died.

But since R2 is actually Padme's droid, as well (remember that he's introduced in the Naboo royal starship), the fact he ends up in Leia's possession makes just as much sense.