(Corrects paragraph 1 to delete reference to document removing Herzer as Redstone's health care agent. Inserts sentence in paragraph 7 to make clear which document was allegedly forged)

Dec 14 (Reuters) - Sumner Redstone's former girlfriend filed a new lawsuit on Monday alleging that the 92-year-old media mogul's signature was forged on a document, supporting her allegation that he was being manipulated in his business and personal affairs.

Redstone is the controlling shareholder of Viacom Inc and CBS Corp, and Manuela Herzer's allegations in lawsuits filed in the past few weeks that he is no longer mentally competent to run the companies has concerned investors.

Redstone had picked Herzer to make his healthcare decisions in case he was not able to but removed her as his health care agent on Oct. 16.

On Nov. 25 Herzer filed a lawsuit in the Los Angeles County Superior Court raising questions about Redstone's mental competence and requested he be medically examined immediately.

The court on Nov. 30 rejected Herzer's request but allowed the case to proceed.

One of the documents Redstone's attorneys filed during the case was the agreement signed by Redstone in October removing Herzer as his health care agent.

Following the removal of Herzer as healthcare agent, an agreement was signed in November allowing her to remove her belongings. Herzer alleges Redstone's signature on this document was forged.

"Sumner's signature on this so-called agreement does not even remotely resemble other signatures of his that I have seen," Herzer said in court documents filed on Monday.

Herzer alleged "a fraud was perpetrated upon this court" and again requested that Redstone's health be checked before a court hearing in January.

Redstone's attorney Gabrielle Vidal said the agreement was not forged and that Herzer's new request was an attempt to get the judge to have Redstone medically examined immediately, and that the court should reject the request.

The judge agreed on Monday to hold a hearing on the issue on Monday, Dec. 21.

Viacom and CBS did not immediately reply to emails seeking comment.

Viacom Chief Executive Philippe Dauman, who replaced Herzer as Redstone's health care agent, said last week that the media mogul was in charge of his own healthcare.

Redstone's physical and mental health have been the subject of intense debate and speculation, partly as he has been largely absent from his companies' earnings calls lately, whereas he previously kicked off the calls with lavish praise for his executives.

The case is in re: Advance Health Care Directive Of Sumner M. Redstone, Superior Court Of The State Of California County Of Los Angeles Central District, No. BP168725. (Reporting by Arathy S Nair and Kshitiz Goliya in Bengaluru and Jessica Toonkel in New York; Editing by Savio D'Souza, Diane Craft)

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