"Bones" has cast a rather important guest role on the show -- Joanna Cassidy will play Marianne, the thus-far unseen mother of Seeley Booth (David Boreanaz).

Although the show has always made it clear that Booth's mother was alive, the heroic FBI agent has rarely mentioned anything about her. The only thing mentioned were that Marianne Booth abandoned her sons and abusive husband 24 years earlier, leaving Seeley and Jared to be raised by their paternal grandfather, Hank (played by Ralph Waite in a couple of "Bones" episodes).

Now, in Season 8, Marianne is back. Her arrival is unexpected and rather inconvenient, according to TVGuide.com, which first reported the casting news.

Joanna Cassidy's long career has included films and many recurring TV roles. In recent years, she has appeared on shows like "Six Feet Under," "Boston Legal," "Hawthorne" and "Body of Proof." There is no date announced for her "Bones" episode.