Bill Cosby had his sexual assault conviction thrown out Wednesday — in a stunning ruling by Pennsylvania’s highest court that found a prosecutor’s decades-old agreement should have shielded him from criminal charges.

The fallen funnyman, 83, is set to walk out of a Philadelphia-area prison a free man after serving more than two years of a three- to 10-year sentence. //

In its 79-page ruling, the State Supreme court found that an agreement with then-Montgomery County District Attorney Bruce Castor Jr. prevented Cosby from being charged for allegedly drugging and molesting Andrea Constand in 2004.

Constand first reported the alleged encounter in 2005 to Castor, who decided not to pursue charges in the case, noting it took her a year to come forward and saying there were inconsistencies in her case.

So Constand sued Cosby in civil court weeks later, and the case was settled for an undisclosed sum.

But as part of that civil case, Castor and Cosby’s camp say they made a behind-the-scenes verbal agreement to have the actor give a deposition on Constand’s allegations in exchange for Cosby never being criminally charged over them.

Cosby had admitted in the deposition that he drugged Constand before performing a sex act on her, although he said it was consensual. //

“When an unconditional charging decision is made publicly and with the intent to induce action and reliance by the defendant, and when the defendant does so to his detriment (and in some instances upon the advice of counsel), denying the defendant the benefit of that decision is an affront to fundamental fairness, particularly when it results in a criminal prosecution that was foregone for more than a decade,” the ruling says.

“For these reasons, Cosby’s convictions and judgment of sentence are vacated, and he is discharged.”