In Ex parte Fierro, 79 S.W.3d 54 (Tex. Crim. App. 2002), a seated and sworn juror was excused because the trial court had erroneously determined that the juror was related to the defendant within the third degree of consanguinity. Even though a claim asserting the erroneous determination of consanguinity had not been raised on appeal, examination of the issue was necessary to our holding that the trial court did not have authority to declare a mistrial in such circumstances. In that case, the law had been well established for many years that venirepersons who are not related to the defendant within the third degree of consanguinity are not excludable, on that basis, from serving as jurors. Fierro involved a simple, noncontroversial, but fatal fact: the trial judge, defense, and prosecution mistakenly believed that, because the venireperson was the defendant's cousin, she was related to him within the third degree of consanguinity.