So far, we don't know much else about who the returning character is — though we do know that it won't be a Denny ghost situation, so it has to be a character who's still alive. So, no, as much as we miss him, it won't be George. No Lexie or Mark, either. Sigh.
That said, there are plenty of old favorites who could still return. For instance, we know that both Shonda Rhimes and Kate Walsh have discussed wanting Addison to return, and Katherine Heigl has openly stated that she wants back on the show to finish up Izzie's arc. Plus, "key character" doesn't have to mean "former regular." We'd be more than happy to see the return of an important guest character — Thatcher Grey is the first one that jumps to mind for us. We still haven't gotten his reaction to Lexie's death.
Which former character do you most hope returns next season? Vote in our poll, and sound off in the comments below!