Oct. 8, 2009— -- Called the Battle of the Blue Bloods, it's a fight to the finish over the fortune of the late millionaire socialite and philanthropist Brooke Astor.
In one corner is her only son, Anthony Marshall, who was convicted of fraud, conspiracy and grand larceny for looting his mother's approximately $180 million fortune as she lay stricken with Alzheimer's disease. Marshall can face up to 25 years in prison. His wife, Charlene, was cast as the villain in her husband's five-month trial.
And who was the star witness against him? Philip Marshall, his son from his first marriage.
The case was set in motion when Philip filed to take over guardianship of his grandmother in 2006. Prosecutors called 72 witnesses to the stand in Anthony's five-month headline-making trial.
"There are people who probably would say, 'Well, how did I do this to my father?'" Philip said in an exclusive interview to air "20/20" Friday. "Quite frankly, what I did was help my grandmother, and he brought this upon himself. ... I don't think that there was anything innocent about what was being done to my grandmother."
"20/20" spoke exclusively to Philip, Tony Marshall and his wife, Charlene, in the weeks before the jury reached a verdict. Tony is now 85. Philip is 56. Brooke Astor died in 2007 at the age of 105.
According to Philip, who became close to his grandmother in later years, Astor was being neglected and his father was at fault. Marshall denied the allegations, calling them "malicious and false."
When Philip filed for guardianship of his grandmother, it set the groundwork for a criminal case against his father on counts of larceny and scheming to defraud. But why did he go to court and not to his father?
"On a good day it would have been great if I could simply talk to my father about this," Philip said. "But that was not the way our relationship was."
"I ended up calling my father and saying that guardianship had been filed. ... Charlene stayed on the line. And I said that I was sorry that I had to, had to do this. And she goes, 'Well, I bet you are.' Something to that effect. At which point I said, 'Well, I'm sorry you made me have to do this.'"
Philip said there were several events that prompted him to take action to protect his grandmother from his own father. He said Tony transferred the title of Astor's beloved Cove End estate in Maine to Charlene; sold a painting she had often said she wanted to go to the Metropolitan Museum of Art and kept a $2 million commission; and he closed her Westchester Country home without her ever knowing.
"She would not have wanted Maine to go to Charlene. I don't want to be presumptuous, but I think that's a fair understanding of the situation," Philip said.
Philip told "20/20" that it was never his intention to make the family disagreement public.
"When we filed we said, this will be settled quietly," he said. "I remember saying to my lawyer, 'Hopefully, you know, this news will be sealed, not will end up on Page Six.' And he said, 'No. It will end up on page one.' And he was right."