Okla. Stat. tit. 84, § 73

Whenever a will or a revocation thereof is duly executed according to the law of the place in which the same was made, or in which the testator was at the time domiciled, the same is regulated as to the validity of its execution, by the law of such place, notwithstanding that the testator subsequently changed his domicile to a place, by the law of which such will would be void.