In a Facebook comment just posted moments ago, Director Peter Jackson confirms Ian Holm’s involvement in The Hobbit films and clarifies the voice at the end of last week’s video:

One comment that came up from the recent video blog was the Bilbo voice at the end—many of you assumed it was Sir Ian Holm. Whilst Ian will be returning as the older Bilbo Baggins in The Hobbit, that recording was actually Martin Freeman’s voice, taken from a script read through we recorded when the cast first arrived. I have to admit, I wasn’t sure who it was when I first heard it, either. Cheers, Peter J

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