Do not fear, the original Gandalf is here.
And he's not the only one...
Per the Hollywood Reporter, Andy Serkis will also be reporting back for motion-capture duty to reprise the role of Gollum, né Sméagol, the decrepit creature who loses the One Ring to Bilbo Baggins in The Hobbit (thereby setting in motion his pursuit of Frodo in The Lord of the Rings).
It was always sort of taken for granted that McKellen and Serkis would return, but it's always nice to have such things in writing.
The very important additions to Peter Jackson's cast come on the heels of news that Elijah Wood and Cate Blanchett will be part of the production, too—although their duties are unclear at this time, since neither character is in J.R.R. Tolkien's Hobbit novel. An offer is out to Orlando Bloom to come aboard, as well.
Cameras are set to start rolling Feb. 14 in New Zealand, so we'll find out soon enough!