Fissures within the famously fractured Sumner Redstone family widened Tuesday when his granddaughter asked to join the contentious court battle over whether the media mogul is mentally competent.

Keryn Redstone, the 34-year-old daughter of Sumner Redstone’s estranged son, Brent, is petitioning the court to allow her to join the lawsuit in support of Redstone’s former companion, Manuela Herzer.

Herzer contends that Sumner Redstone, the controlling shareholder of Viacom Inc. and CBS Corp., is no longer mentally competent.

The move puts Keryn Redstone on the opposite side of the legal dispute from her 92-year-old grandfather, whom she calls “Grumpy,” and her aunt, Shari Redstone. Revelations contained in the new court papers included Keryn Redstone’s allegations that her aunt, Shari Redstone, had threatened her and acted insensitively toward Sumner Redstone.


In her 11-page declaration, Keryn Redstone described a tense 2014 hospital drama that included a shouting match between Sumner Redstone, whom she called “Grumpy,” and his daughter, Shari Redstone. The two argued about whether Sumner Redstone should have a feeding tube installed, which he did when he began having difficulty swallowing.

“I clearly heard Shari state her beliefs as to what should happen to Grumpy. She said, ‘If he gets sick, don’t take him to the hospital. Let him die at home.’ Grumpy, being Grumpy, interjects -- ‘I don’t want to die,” Keryn Redstone said.

A representative of Shari Redstone said that neither Shari “nor anyone in her family, opposed the insertion of a feeding tube.”

In a separate statement, Shari Redstone, who is vice chair of Viacom and CBS, blasted her niece’s efforts to join the lawsuit as a petitioner alongside Herzer, the mogul’s former companion.


“This is not the first time that Keryn has sued an elderly relative for her own financial gain,” Shari Redstone said in the statement. “I am sad and disappointed that Keryn has chosen to align herself with Herzer against my father. I will not dignify the absurdity of Keryn’s false claims with any further response.”

Attorneys representing Sumner Redstone were not immediately available for comment.

Keryn Redstone’s allegations added further turmoil to a family with a long history of infighting and could have broader ramifications over the future of Viacom and CBS. The Redstone family controls nearly 80% of the voting shares of the two companies that boasts such properties as Paramount Pictures, CBS broadcast network, Showtime, MTV, Nickelodeon and Comedy Central.

The latest motion asks Los Angeles County Superior Court Judge David J. Cowan to allow Herzer to amend her original complaint, filed in late November, which seeks to have the ailing media mogul declared mentally incompetent.


The lawyers asked the judge to allow Keryn Redstone to join the lawsuit as a petitioner alongside Herzer. Herzer’s attorneys described the Keryn Redstone declaration as “a game changing event in this litigation.”

They also asked the judge to authorize an examination of Redstone by another physician, hired by Herzer’s side.

Cowan is expected to rule this week on the motions.

Keryn Redstone, in her declaration, also described discovering “five or six people operating a larger shredder” in her grandfather’s Beverly Park home when she visited in late October, after Herzer was forced from the picture. Keryn Redstone said she was told to stay out of the shredding room, and she said she didn’t know what documents were being destroyed.


The latest court maneuver also seeks to invalidate legal documents signed this month that named Shari Redstone as the agent in charge of Redstone’s advance healthcare directive should the mogul become incapacitated.

Herzer and Keryn Redstone appear to be teaming up to try to prevent Shari Redstone from overseeing Redstone’s affairs. They asked the judge to invalidate action on April 4 in which Sumner Redstone named Shari Redstone as his healthcare proxy, replacing Viacom Chief Executive Philippe Dauman.

In her declaration, Keryn Redstone described what she called a close relationship with her grandfather. She said the two shared a love of “film, art, dogs and tennis -- which we loved playing together.

“Even as he aged, Grumpy would regularly beat me at tennis,” Keryn Redstone wrote.


In recent years, she said that she has been a frequent visitor to her grandfather’s Beverly Park mansion. She began spending more time in Los Angeles last fall after Redstone’s former girlfriend, Sydney Holland, was forced out of Redstone’s home.

Keryn Redstone said she has known Herzer, 51, for more than 15 years and that her grandfather cared for Herzer deeply. Herzer cared for Redstone and oversaw his household affairs until she was booted from Sumner Redstone’s home in mid-October.

Herzer filed the lawsuit in late November, contending that she was wrongly removed from Redstone’s life. She contends that Redstone no longer is able to make decisions for himself and that she should be restored to a position of authority.

Keryn Redstone also described her grandfather’s decline.


She said last fall the aging mogul developed a fixation on another woman, whom he wanted to have sex with. Keryn Redstone, in the declaration, accused one of Redstone’s nurses, Jeremy Jagiello, of coordinating liaisons between Sumner Redstone and the other woman.

Keryn Redstone alleged that Jagiello exerted control over the elderly mogul because he became one of the few people who could translate for Sumner Redstone, who has great difficulty speaking intelligibly.

“When I visited Grumpy again in December, there was a definite, perceptible change in the mood in Grumpy’s house,” Keryn Redstone said. “It began to feel like a prison.”

The granddaughter also noted that she has not seen Sumner Redstone in two months.


During a visit in February, she said the family screened the movie, “Deadpool,” at Redstone’s house. “He cried during the opening credits,” she said.

Keryn Redstone said she has asked to see her grandfather, and that Redstone’s corporate secretary suggested that Keryn Redstone instead reach out to the mogul’s ex-wife, Paula Fortunato, who is said to be back in the picture.

“I have not seen my Grumpy since February. I know his condition has continued to worsen and I want nothing more than to see him again,” Keryn Redstone said.

Her father, Brent Redstone, parted ways with his father and sister a decade ago after Sumner Redstone appeared to favor his daughter in business dealings. Brent Redstone sued the family business, National Amusements Inc., and received a $250-million settlement. He relinquished his stake in the holding company.


Brent Redstone’s two daughters are among the five beneficiaries of the Sumner M. Redstone National Amusements Inc. Trust that holds the controlling shares of Viacom and CBS. The Redstone family owns nearly 80% of the voting shares of the two media entities.

Shari Redstone’s three children also are beneficiaries of the Sumner M. Redstone NAI Trust. Shari Redstone and her younger son, Tyler Korff, are among the trustees who will make decisions about the family’s holdings in CBS and Viacom.

The Hollywood Reporter first reported on the filing regarding Keryn Redstone.

The injection of Keryn Redstone into the court case could put additional pressure on the Sumner Redstone camp to try to hammer out a settlement to avoid the trial that would delve into the family’s fractured dynamics.


The two sides made progress toward a settlement but talks fell apart this month, and both sides geared up to prepare for the trial that’s scheduled for May 6.

meg.james@latimes.com

Twitter: @MegJamesLAT

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