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It was a strange sight in the rarified world of Manhattan high society: The 83-year-old son of Brooke Astor, the grand dame of New York philanthropy, standing in a courtroom accused of plundering her fortune.

As Anthony Marshall arrived to face the charges, his wife, Charlene, leaped up from her front-row seat and started patting his head and adjusting his white hair. "We'll be all right," she said.

Marshall, a former diplomat and Tony award-winning theater producer, pleaded not guilty Tuesday to preying on his Alzheimer's-stricken, centenarian mother, looting her $198 million estate and inducing her to sign a new will leaving her vast fortune to him.

The indictment alleges that Marshall spirited artworks out of Astor's home, gave himself a $1 million raise for serving as her financial adviser and spent his mother's money on a laundry list of extravagant items — including $52,000 in salary for the captain of his 55-foot yacht. Prosecutors also say he had Astor amend her will to leave him the $60 million-plus part of her estate that she intended for charity.

"Despite his mother's generosity when she was well, he used his position of trust to steal from her," Assistant District Attorney Elizabeth Loewy said.

If convicted of the most serious charge, grand larceny, Marshall could be sentenced to 25 years in prison. Marshall has denied all allegations that he abused his mother's trust, saying he cared about her more than anyone.

"Tony Marshall faithfully and effectively managed his mother's affairs for more than 25 years, increasing the value of her investments from $19 million to $82 million," said a statement issued by the defendant's lawyer, Kenneth Warner.

Marshall was released and ordered to appear in court Jan. 30.

The indictment charges Marshall with grand larceny, criminal possession of stolen property, scheme to defraud, falsifying business records, offering a false instrument for filing and conspiracy. Marshall's former attorney, Francis X. Morrissey Jr., was indicted on charges of forgery, criminal possession of a forged instrument, scheme to defraud and conspiracy.

Morrissey's lawyer, Michael S. Ross, told The New York Times his client was out of the country but returning to surrender to authorities Friday.

The indictment charges that Marshall and Morrissey "took advantage of Mrs. Astor's diminished mental capacity in a scheme to defraud her and others out of millions of dollars," District Attorney Robert Morgenthau said.

As early as 2001, Astor's doctors had told Marshall that his mother suffered from Alzheimer's disease, that her ability to understand complex issues was limited, and that her condition would worsen, Morgenthau said.

Three years later, the prosecutor said, Marshall and Morrissey conspired to have Astor's longtime attorney fired and to have her sign an updated will that left Marshall virtually everything.

One of Marshall's sons, Philip, prompted the criminal investigation last year after he accused his father of neglecting Astor's care and stealing her money. Astor died in August at age 105.

Despite his role in launching the case, Philip Marshall said Tuesday he was "shocked" at the charges.

"I sincerely hope there is a way justice can be achieved without my father going to jail," Marshall, 54, told the Daily News as he took a walk near his home in South Dartmouth, Mass.

The indictment alleges that Marshall robbed Astor's estate in ways ranging from salary increases to art sales.

Prosecutors say he falsely told Astor she was running out of money to persuade her to sell a Childe Hassam painting, "Up the Avenue from 34th Street," for $10 million; he allegedly took $2 million as a sales commission. He also is accused of taking two works of art, worth about $500,000 each, from Astor's house while she still lived there.

Marshall also used Astor's money in 2005 to boost his salary for serving as her financial adviser from $450,000 to about $1.4 million, prosecutors say.

Astor, known for decades as the doyenne of New York society and philanthropy, gave away nearly $200 million to institutions such as the New York Public Library, Carnegie Hall and other causes.

In the final year of her life, the nasty family feud over her care was splashed all over the city's tabloids — including allegations that she was forced to sleep in a torn nightgown on a couch that smelled of urine while subsisting on a diet of pureed peas and oatmeal. Those allegations were never substantiated.