There's a well-documented phenomenon in serialized TV shows (one 'LOST' suffered from quite a bit), in which SAG rules dictate that any guest actor must be listed in show's opening credits, thereby ruining any surprise appearances.  Those who watched the first half of 'Fringe's season finale "Brave New World" this past Friday may have had the return of a certain villain spoiled (yay for oblivious viewers!) in advance, but what does the reappearance mean?

That's right, Leonard Nimoy has returned!  In spite of repeated insistence that his acting career is over (apart from the occasional voice-over gig), those witnessing "Brave New World, Part 1" were treated to the reveal that the actual villain pulling David Robert Jones ('Mad Men's Jared Harris)' strings was none other than Walter Bishop's former partner William Bell!  To be fair, he's a little more on the dark side this time.

Of course, William Bell had supposedly died in 'Fringe's current timeline as well, though here of a car accident rather than sacrificing himself to help get the Fringe team home from the other side in season 2 finale "Over There."  Bell was also glimpsed in the future-centric episode "Letters of Transit," though there appeared as CG stock footage, a development that the writers didn't need to explain just yet.

Either timeline you subscribe to, both Nimoy and Bell are back, and ready to take us into the second half of the season 4 finale!  Has "Belly" gone completely mad with power?  Will Astrid recover from her injuries last week?  And what does it have to do with Olivia's supposed death, and "what William Bell did to her" in the future?

Check out a brand new featurette of John Noble and Leonard Nimoy discussing the relationship between Walter Bishop and William Bell, and taking us into the season 4 finale this Friday!  Don't forget to catch the last episode before the 13-episode fifth season this fall, and tell us what you're most excited to see in the comments!