Anthony Marshall, the son and heir of New York philanthropist Brooke Astor who went to prison at age 89 for his handling of her estate, has died. He was 90.

He died yesterday in New York, the Associated Press reported, citing his lawyer, Kenneth Warner. No cause was given.

Marshall was a former U.S. ambassador who said he had worked on the CIA’s U-2 spy-plane program in the 1950s. He was best known as the only child of Astor, a socialite who was a major funder of the Metropolitan Museum of Art and New York Public Library.

Controversy swirled over her fortune for several years before her death in 2007 at age 105, after suffering from Alzheimer’s disease. Her will was changed several times in the years leading up to her death to give Marshall a bigger share of her fortune, valued by the New York State Attorney General at more than $100 million.

Marshall was co-executor of the estate and also managed his mother’s finances for many years. Marshall was initially investigated for elder abuse. No charges stemmed from that, though Marshall and an Astor family lawyer, Francis X. Morrissey Jr., were convicted in 2009 on charges including grand larceny over changes to the will.

After a rejected appeal, Marshall received a sentence of one to three years in prison and reported on June 21, 2013. He was released on medical parole two months later.