"I'll get by," he said, "but my heart goes out for the thousands and thousands of employees and their families who are shareholders, and not only in the United States but worldwide."
He blamed AIG's current board of directors. He has been at loggerheads with the company since stepping down in 2005 and has been a regular critic of its management.
"After I left the company, all the risk management procedures that we had in place were obviously dismantled," he told "GMA." "I can't explain that. There was a new board of directors. One should be asking that board of directors what they did and why."
Speaking on the condition of anonymity, one board member said Greenberg was bitter and lying, and called the former CEO's comments "unadulterated nonsense."
"[It is] extraordinary he would go public and say something like this. He's just trying to purify his reputation," the board member said.
Shelp, who for more than a decade occupied an office down the hall from Greenberg at AIG, said he believed the company began investing in credit swaps tied to mortgages while Greenberg was still in charge.
"He was CEO at the time. The company has been doing credit swaps for more than three years," Shelp said. "I don't know what risk-management control would have been removed, but it doesn't make any sense that the board would do that."
Greenberg's losses come just four days after he settled a lawsuit filed by some AIG shareholders, including the Teachers Retirement System of Louisiana, over the same shady dealings that got him investigated -- but never prosecuted -- by Spitzer.
"The truth is, I can't help but feel sorry for him," said Stuart Grant, the lawyer representing the Louisiana teachers who won a $115 million settlement. "Ninety-five percent of his assets have disappeared. Maybe he's left with $1 billion, maybe several hundred million, to most mortals that's a heck of a lot of money, but think about all that work over all those years, and now it's all gone."
ABC News's Eileen Murphy contributed to this report.