Sumner Redstone’s granddaughter wants to join a lawsuit challenging Redstone's mental competency. Reuters reports that Keryn Redstone, daughter of the CBS and Viacom executive chairman’s estranged son Brent Redstone, filed a declaration Tuesday saying the 92-year-old media mogul was a “prisoner in his own home” after Redstone´s former companion, Manuela Herzer, was removed as his health care agent.

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