Darryl McCauley, who worked as the funnyman's business manager for almost five years, was arrested in Massachusetts in December 2008, accused of stealing from Cook by forging a $3 million (£2 million) cheque to himself.
On Wednesday (13Oct10) he pleaded guilty to 27 counts of larceny, three counts of forgery, and single counts of embezzlement, uttering and conspiracy in a Massachusetts court room. He was sentenced to between five and six years in prison.
Attorney General Martha Coakley says in a statement, "For several years, Mr. McCauley abused his position as a family member to gain Mr. Cook's trust, and stole millions of dollars for his own personal gain. We hope that today's sentence will act as a deterrent, and our office will continue to investigate and prosecute these cases."
McCauley will also serve 10 years' probation once he's released from jail, reports E! Online.
Meanwhile Cook's sister-in-law, who is married to McCauley, has been charged with larceny by scheme and receiving/concealing stolen property for allegedly aiding and abetting her husband. She is due in court on 26 October (10).