Shocking new details have emerged about the sudden death of beloved actress Diane Keaton – RadarOnline.com can reveal she was secretly battling hereditary dementia in her final months and that the final downswing was so rapid and severe that even her closest friends didn't realize what was happening.

Although the family announced that the final cause of death on October 11 at age 79 was from pneumonia, sources said loved ones chose to keep the news of the Annie Hall Oscar winner's debilitating brain disease from the public. Article continues below advertisement

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"She'd been struggling quietly for some time," one longtime

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