In In Ex parte Stephenson, 722 S.W.2d 426, 428 (Tex. Crim. App.1987), the district attorney admitted at the habeas hearing that he, as well as the defendant and defense counsel, was mistaken about the applicable parole law. Stephenson, 722 S.W.2d at 427. He stated that what he sought was a "40 year" sentence, but that he had been willing to waive a deadly weapon finding so that the defendant would be eligible for parole without being required to serve 1/3 of the sentence "flat time." In short, "he believed he had found a way to get 40 years and put the applicant in the position 'that he had agreed to on his guilty plea.'" Id. Thus, in Stephenson, the mutual misunderstanding about parole law and its essential part of the plea agreement was implicit when the defendant actually made the plea, but became explicit when the prosecutor testified to its terms at the habeas hearing. Stephenson stands for the proposition that, when the record clearly shows that a mistaken understanding of parole eligibility formed an essential element of the plea agreement, and that misunderstanding makes the agreement impossible to fulfill, the plea is involuntary. Parole eligibility must be an essential element of the plea agreement, though it need not be formally incorporated into the record at the time the plea is consummated.