In Duhig v. Peavey-Moore Lumber Co., 135 Tex. 503, 144 S.W.2d 878 (Tex. 1940), a third party owned an outstanding one-half mineral interest in certain land, and the grantor owned the surface and the remaining one-half mineral interest. The grantor conveyed the surface to the grantee by warranty deed but reserved one-half of all the minerals under the land. Id. The grantor and grantee both claimed the one-half mineral interest that was not owned by the third party. Id. at 879. The Texas Supreme Court concluded the grantee owned the surface and a one-half mineral interest, the third party owned the outstanding one-half mineral interest, and the grantor owned nothing. Id. at 880. In reaching that conclusion, the court employed a two-step analysis under principles of estoppel. Id. The court observed the grant clause gave the grantee all of the surface and a one-half mineral interest but the reservation clause reserved a one-half mineral interest in the grantor. Id. Because the grantor purported to retain a one-half mineral interest and the other one-half mineral interest was owned by a third party, the grantor breached the clause warranting title to a one-half mineral interest. Id. By analogy to the doctrine of estoppel by deed against assertion of an after-acquired title, the court held the grantor was estopped to assert the reservation of a one-half mineral interest. Id.