The media mogul Sumner M. Redstone was in the middle of a bitter divorce from his wife of 52 years in December 2000 when he was spotted with a decades-younger woman at the New York premiere of the Paramount movie “What Women Want.’’

His companion was Manuela Herzer, then a 36-year-old single mother of three. The pair met the previous year, and they dated for about two years. When he asked her to marry him in 2000, she declined.

Yet Herzer remained in the orbit of Redstone’s life as a friend, even as he cycled through another marriage and a series of girlfriends. He lavished gifts, real estate, and money on her — more than $70 million in cash and other assets since 2009. He named her a beneficiary of his personal trust, listing her as “family.’’ Upon his death, he planned to leave her an additional $50 million and his $20 million Los Angeles mansion, according to various court filings.

Now Herzer has filed a salacious lawsuit challenging Redstone’s mental competence. She filed the suit in November, not long after she was suddenly ejected from Redstone’s life and his home, where she had maintained a residence for about two years. She also was removed from his will and from a directive that would have given her supervision of his health care.

The legal battle, filled with claims about Redstone’s sexual desires, incontinence, and demands to eat steak while on a feeding tube, is scheduled for trial starting Friday in Los Angeles County Superior Court, exactly three weeks before his 93rd birthday.

This real-life soap opera has captivated Hollywood and Wall Street. While the dispute concerns Redstone’s personal affairs, the outcome could have major implications for his $42 billion media empire, which includes two of the world’s largest entertainment companies, Viacom and CBS, both still controlled by Redstone.

A ruling by Judge David J. Cowan that Redstone is not competent would set off a contentious battle for power across Redstone’s businesses.

At the center of it all is Herzer, now 51, who claims in the suit that Redstone lacked mental capacity and was under the undue influence of his daughter, Shari Redstone, when he changed his health care plan.

The court is expected to hear video testimony from Redstone, as well as from his daughter, doctors, and nurses; Herzer; and Philippe Dauman, chief executive of Viacom.

Robert N. Klieger, a lawyer for Redstone, said in a statement that the case was all about money for Herzer.

“For Mr. Redstone, it is about his ability to decide who will make the most important health care decisions in his life,’’ Klieger added. “Some things are more important than money.’’

Herzer has said the suit is solely about Redstone’s well-being. She was introduced to him by one of his old friends in 1999, about five years after her bitter divorce from Eric Chamchoum, a Nigerian-born telecommunications executive who is part of a dynastic Lebanese family.