Bruce Castor's assertion in a lawsuit Thursday is the first time anyone has put a value on the settlement.
Castor's lawsuit says accuser Andrea Constand and her lawyers harmed his reputation and cost him a chance to return as district attorney in suburban Philadelphia.
The settlement's terms are confidential. The lawsuit doesn't explain how Castor would know how much it was. His and Constand's lawyers didn't immediately return messages.
Castor has testified that his decision to not prosecute was intended to let Cosby speak freely at a civil deposition.
A new prosecutor charged Cosby after excerpts from that testimony were made public. A June trial ended in a mistrial. A retrial is scheduled for April.
The Associated Press does not typically identify people who say they are victims of sexual assault unless they grant permission, which Constand has done.
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