The 38-year-old star has joined the cast of the film, which tells the heartbreaking story of how a couple copes when the wife is diagnosed with early onset Alzheimer's.
Claudia Ferri and Dana Ashbrook will portray the couple, while King will play the neurologist who treats the wife, according to The Hollywood Reporter.
Drew Pollins is directing the movie, based on the book of the same name by Pat Moffat.
Besides acting, King has also turned to writing and directing, with her directorial debut "Latch Key" (2011).
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