Sir Ian McKellen is speaking out in a new interview about Benedict Cumberbatch’s role as a dragon in Desolation of Smaug as well as why the story needs to be split into three movies.

As good J.R.R. Tolkien and Peter Jackson fans know, McKellen plays Gandalf in The Lord of the Rings and The Hobbit trilogies.

Metro sat down with the actor and first pressed him on why The Hobbit prequel, which is the smallest book out of all of Tolkien’s Lord of the Rings tomes, has to be three parts. “I thought it was pushing it to make even two films, which is what we were originally doing,” he said, “but then I realised that one of the reasons it does spread into a trilogy is that Tolkien can describe something in under a paragraph that will take far longer to replicate on-screen. For instance, ‘the army advances’; that’s only three words but involves a lot of visual action. It isn’t that the book has been expanded I suppose, it’s that it has gone into all its detail.”

He also spoke about the second Hobbit film The Desolation of Smaug which will feature Benedict Cumberbatch (Sherlock, Star Trek Into Darkness) as Smaug himself. He himself is unsure of how it’s possible to portray a dragon. “Doing motion capture for a part such as that is tricky, I mean how do you play a dragon? Then again, before Lord Of The Rings people were saying how on Earth do you play a Gollum?’”

Time will tell how Cumberbatch pulled it off. “None of us have seen the finished Smaug yet but I saw Benedict Cumberbatch’s screen test and it was very impressive,” he said.

The Hobbit: The Desolation of Smaug opens in theaters December 13, 2013. So far we’ve only seen one official still from the film, though Jackson hosted a first look in March.