When on trial in partition proceeding, defendants, having denied tenancy in common, plead sole seizin, non ienent insimul, by reason of deed to them from common source, and, the proceeding-having been transferred to the civil issue docket for trial, plaintiffs fail before the jury in their attack upon that deed on the ground that the grantor did not have sufficient mental capacity, at the time, to execute it, and final judgment sustaining the plea of sole seizin is entered, is such judgment res adjudicata, and, when pleaded, a bar to prosecution of subsequent independent action to set aside and cancel the deed for undue influence exerted by the grantees?
*204Tbe uniform decisions of this Court are consonant with an affirmative answer.
Tenancy in common in land is necessary basis for maintenance of special proceeding for partition by petition to the Superior Court. C. S., 3213, 3215. Gregory v. Pinnix, 158 N. C., 147, 73 S. E., 814. When tenancy in common is denied and there is a plea of sole seizin, non tenent insimul, the proceeding in legal effect is converted into an action in ejectment and should be transferred to the civil issue docket for trial at term on issue of title, the burden being upon the petitioners to prove their title as in ejectment. C. S., 758. Huneycutt v. Brooks, 116 N. C., 792, 21 S. E., 558; Alexander v. Gibbon, 118 N. C., 796, 24 S. E., 748; Bullock v. Bullock, 131 N. C., 29, 42 S. E., 458; Sipe v. Herman, 161 N. C., 108, 76 S. E., 556; McKeel v. Holloman, 163 N. C., 132, 79 S. E., 445; Dilmore v. Rexford, 165 N. C., 620, 81 S. E., 994; Lester v. Harward, 173 N. C., 83, 91 S. E., 698; Moore v. Miller, 179 N. C., 396, 102 S. E., 627; Higgins v. Higgins, supra.
The doctrine of estoppel, with its conclusive effect, applies to proceedings in partition which are no longer merely possessory actions but are proceedings in which the title can be litigated. Armfield v. Moore, 44 N. C., 157; Carter v. White, 134 N. C., 466, 46 S. E., 983; McCollum v. Chisholm, 146 N. C., 18, 59 S. E., 160; Buchanan v. Harrington, 152 N. C., 333, 67 S. E., 747; McKimmon v. Caulk, 170 N. C., 54, 86 S. E., 809; Bank v. Leverette, 187 N. C., 743, 123 S. E., 68; Wallace v. Phillips, 195 N. C., 665, 143 S. E., 244.
In McKimmon v. Caulk, supra, Allen, J., said: “The primary purpose of partition proceedings is to sever the unity of possession, but the parties may put the title in issue, and when they do so, and the title is adjudicated, the judgment is conclusive and binding.” Buchanan v. Harrington, supra; Wallace v. Phillips, supra; Crawford v. Crawford, 214 N. C., 614, 200 S. E., 421.
The general rule is that judgment of a court of competent jurisdiction is final and binding upon parties and privies. Ordinarily, to constitute a judgment an estoppel there must be an identity of parties as well as of the subject matter. In scope of operation with respect to the subject matter “it is not only final as to the matter actually determined, but as to every other matter which the parties might litigate in the cause, and which they might have had decided. . . . The court requires parties to bring forward the whole case, and will not, except under special circumstances, permit the same parties to open the same subject of litigation in respect to matters which might have been brought forward as part of the subject in controversy . . . The plea of res adjudicata applies, except in special cases, not only to the *205points upon which the court was required by the parties to form an opinion and pronounce a judgment, but to every point which properly belonged to the subject in litigation and which the parties, exercising reasonable diligence, might have brought forward at the time and determined respecting it.” Herman on Estoppel and Res Judicata,-sec. 122, p. 130, and sec. 123, p. 131.
To like effect are decisions of this Court. Tuttle v. Harrill, 85 N. C., 456; Wagon Co. v. Byrd, 119 N. C., 460, 26 S. E., 144; Buchanan v. Harrington, supra; In re Will of Lloyd, 161 N. C., 557, 77 S. E., 955.
Applying these principles to the present action, there are here both identity of parties and identity of subject matter. The plaintiffs here were of petitioners, and the defendants here were of defendants in the former proceeding. Likewise, the title to the same land as affected by the same deed was in issue and involved in the former proceeding as in the case at bar. In the former, plaintiffs attack the deed for mental incapacity of the grantor, and in the present action, for undue influence exerted upon the grantor by the grantee. These grounds of attack are pertinent to the same subject and germane to the same issue.
When in answer filed in partition proceeding the defendants R. L. Higgins and wife pleaded sole seizin, and based that plea upon the deed from J. N. Higgins, the source under which plaintiffs claim title, plaintiffs were put upon notice that the title to the land was in issue and that the defendants relied upon that deed as the basis for their claim. The way was then open to plaintiffs to attack the deed upon any and all existing grounds, both legal and equitable. It was incumbent upon them to bring forward and assert their whole case with respect thereto. They relied upon their right, upon general issue of title, to offer evidence in attack upon the legality of the deed in question solely upon the ground of mental incapacity of J. N. Higgins to execute the deed. If the plaintiffs desired to attack the deed by reason of undue influence exerted upon J. N. Higgins by the defendants, the door was open to them to plead same and to offer evidence in support thereof. Toler v. French, 213 N. C., 360, 196 S. E., 312, and cases there cited. As to mental incapacity, parol evidence may be offered without appropriate allegation. Alley v. Howell, 141 N. C., 113, 53 S. E., 821; Higgins v. Higgins, supra. But as to undue influence, parol evidence will not be received unless there be appropriate allegations. Alley v. Howell, supra; Toler v. French, supra. Both could have been asserted and relied upon in the former action. But, having elected to attack the deed solely upon the ground of mental incapacity, plaintiffs have had their day in court, and are deemed to have waived the right to allege and assert undue influence. The jury found that J. N. Higgins had sufficient *206mental capacity at the time to execute the deed. Final' judgment declaring the defendants sole owners of the land in question has been entered. After judgment it is too late for plaintiffs to set up new and different ground upon which to attack the same deed. Graves v. Barrett, 126 N. C., 267, 35 S. E., 539.
The judgment below is