Carl Glenn Pickard (“plaintiff’) appeals from the trial court’s order denying the annulment of his marriage to Jane Edwards Pickard (“defendant”). As discussed below, we affirm.
Hawk Littlejohn (“Littlejohn”), a Cherokee Indian, married plaintiff and defendant in the Native American tradition on 7 June 1991. *194Plaintiff is a physician employed by the University of North Carolina at Chapel Hill (“UNC”). Plaintiff had met Littlejohn at the UNC medical school where Littlejohn lectured as a Cherokee shaman or “medicine man.” Littlejohn performed healings and conducted ceremonies in accordance with Cherokee traditions. Littlejohn also possessed a certificate stating that he was ordained as a minister in the Universal Life Church.
Defendant initially desired to be married in a traditional Christian ceremony. Plaintiff persuaded defendant to be married in the Cherokee tradition with Littlejohn performing the ceremony. When Littlejohn performed the wedding ceremony, both the parties believed the ceremony was legally sufficient to bind plaintiff and defendant as husband and wife. Littlejohn conducted the parties’ ceremony in accordance with the Cherokee marriage tradition. The parties received a North Carolina license and certificate of marriage on 3 December 2002, which was filed in the Caswell County Register of Deeds office.
After the ceremony, and for the next eleven years, the parties lived together and conducted themselves as husband and wife. In 1998, plaintiff initiated proceedings to adopt defendant’s adult biological daughter. In his amended petition for adult adoption, and as a requisite of the adoption, plaintiff provided a sworn statement that he was “the stepfather of the adoptee, having married her natural mother.” Plaintiff also listed his marital status as “married.” The clerk of superior court in Caswell County filed an amended decree of adoption on 9 November 1998, based on plaintiff’s assertions.
On 9 April 2002, the parties separated. On 23 April 2002, plaintiff filed a complaint for annulment of his eleven-year marriage to defendant. On 23 May 2002, defendant answered and denied that plaintiff was entitled to an annulment. After plaintiff presented his evidence, defendant moved for a directed verdict. Counsel for both parties argued and briefed defenses of collateral estoppel and res judicata. On 3 February 2003, the court informed the parties through correspondence that defendant’s motion for directed verdict was denied.
On 28 May 2003, defendant filed a motion to amend the pleadings alleging the defenses of collateral estoppel and res judicata. A delay occurred due to the illness of the presiding judge. On 7 May 2004, defendant presented evidence. At the conclusion of defendant’s evidence, defendant’s motion for a directed verdict was denied.
*195On 27 September 2004, the trial court filed a judgment concluding that the marriage ceremony was not properly solemnized because Littlejohn was not qualified to perform a marriage ceremony. The court denied plaintiff’s claim for annulment because plaintiff had asserted under oath, judicially admitted and proved his marriage to defendant in the adoption proceeding. Plaintiff appeals. Defendant argues cross assignments of error.
 Plaintiff first argues that the trial court erred in allowing defendant’s motion to amend her answer to include the defenses of estoppel, collateral estoppel and res judicata. We disagree.
“The trial court’s decision regarding a party’s motion to amend the pleadings will not be disturbed on appeal unless an abuse of discretion is shown.” Stetser v. TAP Pharm. Prods., Inc., 165 N.C. App. 1, 30, 598 S.E.2d 570, 589 (2004). After the filing of a responsive pleading, “a party may amend his pleading only by leave of court or by written consent of the adverse party; and leave shall be freely given when justice so requires.” N.C. Gen. Stat. § 1A-1, Rule 15(a) (2003). “Rule 15(a) contemplates liberal amendments to the pleadings, which should always be allowed unless some material prejudice is demonstrated.” Stetser, 165 N.C. App. at 31, 598 S.E.2d at 590. “Some of the reasons for denying a motion to amend include undue delay by the moving party, unfair prejudice to the nonmoving party, bad faith, futility of the amendment, and repeated failure to cure defects by previous amendments.” Id. “The objecting party has the burden of satisfying the trial court that he would be prejudiced by the granting or denial of a motion to amend.” Watson v. Watson, 49 N.C. App. 58, 60, 270 S.E.2d 542, 544 (1980).
Here, the court’s allowance of the amendment did not prejudice plaintiff’s ability to present evidence related to the additional defenses. The court deferred its ruling on amendment until it had heard evidence on estoppel, and permitted both parties to submit briefs if they desired. Plaintiff never argued at trial that he was prejudiced in his ability to present evidence on these issues; he merely contended that the issues could not be considered because they had not been included in the original answer. We conclude that the court did not abuse its discretion in permitting amendment of defendant’s answer.
 Plaintiff argues that the trial court erred when it denied the annulment. We do not agree.
A party to a marriage may seek an annulment in accordance with N.C. Gen. Stat. § 50-4 (2003). The statute provides:
*196The district court, during a session of court, on application made as by law provided, by either party to a marriage contracted contrary to the prohibitions contained in the Chapter entitled Marriage, or declared void by said Chapter, may declare such marriage void from the beginning, subject, nevertheless, to G.S. 51-3.
N.C. Gen. Stat. § 50-4 (2003). This Court stated in Geitner v. Townsend, “[a] voidable marriage is valid for all civil purposes until annulled by a competent tribunal in a direct proceeding, but a void marriage is a nullity and may be impeached at any time.” 67 N.C. App. 159, 161, 312 S.E.2d 236, 238, disc. review denied, 310 N.C. 744, 315 S.E.2d 702 (1984). N.C. Gen. Stat. § 51-1 (1977) was the statute in effect that governed marriage ceremonies when plaintiff and defendant were married. The statute required the parties to “express their solemn intent to marry in the presence of (1) an ordained minister of any religious denomination, or (2) a minister authorized by his church or (3) a magistrate.” State v. Lynch, 301 N.C. 479, 487, 272 S.E.2d 349, 354 (1980) (internal quotation marks omitted).
Our Supreme Court has stated: “[u]pon proof that a marriage ceremony took place, it will be presumed that it was legally performed and resulted in a valid marriage.” Kearney v. Thomas, 225 N.C. 156, 163, 33 S.E.2d 871, 876 (1945). The burden of proof rests upon plaintiff to prove by the greater weight of the evidence grounds to void or annul the marriage to overcome the presumption of a valid marriage. Townsend, 67 N.C. App. at 163, 312 S.E.2d at 239.
We begin by noting that the dissent states that Littlejohn was an ordained minister. However, although the trial court found that Littlejohn possessed a certificate stating that he was ordained by the Universal Life Church, “[t]hat at no time was Hawk Littlejohn a minister of the gospel licensed to perform marriages.” The court also found and concluded that Littlejohn’s ordination was not cured by N.C. Gen. Stat. § 50-1.1. Because these findings have not been challenged, they are conclusive on appeal. Rite Color Chemical Co. v. Velvet Textile Co., 105 N.C. App. 14, 22, 411 S.E.2d 645, 650 (1992).
“The well-established rule is that findings of fact by the trial court supported by competent evidence are binding on the appellate courts even if the evidence would support a contrary finding.” Scott v. Scott, 336 N.C. 284, 291, 442 S.E.2d 493, 497 (1994) (citing In re Estate of Trogdon, 330 N.C. 143, 147, 409 S.E.2d 897, 900 (1991)). “As to findings in a bench trial, we review matters of law de novo.” State Farm *197 Fire & Cas. Co. v. Darsie, 161 N.C. App. 542, 548-49, 589 S.E.2d 391, 397 (2003), disc. review denied, 358 N.C. 241, 594 S.E.2d 194 (2004) (citing Graham v. Martin, 149 N.C. App. 831, 561 S.E.2d 583 (2002)), disc. rev. denied, 358 N.C. 241, 594 S.E.2d 194 (2004).
In its judgment, the trial court concluded as law that although the parties’ marriage was not properly solemnized pursuant to statute, plaintiff was estopped from obtaining an annulment on several grounds, including judicial estoppel, quasi-estoppel, collateral estoppel and res judicata. As discussed below, we conclude that judicial estoppel applies here and affirm the trial court’s judgment on that basis.
“[judicial estoppel seeks to protect courts, not litigants, from individuals who would play ‘fast and loose’ with the judicial system.” Whitacre P’ship v. BioSignia, Inc., 358 N.C. 1, 26, 591 S.E.2d 870, 887 (2004). In addition, “because of its inherent flexibility as a discretionary equitable doctrine, judicial estoppel plays an important role as a gap-filler, providing courts with a means to protect the integrity of judicial proceedings where doctrines designed to protect litigants might not adequately serve that role.” Id. In adopting the framework of the United States Supreme Court as stated in New Hampshire v. Maine, 532 U.S. 742, 149 L. Ed. 2d 968 (2001), the North Carolina Supreme Court has set forth three factors to be considered in applying judicial estoppel:
First, a party’s subsequent position must be clearly inconsistent with its earlier position. Second, courts regularly inquire whether the party has succeeded in persuading a court to accept that party’s earlier position, so that judicial acceptance of an inconsistent position in a later proceeding might pose a threat to judicial integrity by leading to inconsistent court determinations or the perception that either the first or the second court was misled. Third, courts consider whether the party seeking to assert an inconsistent position would derive an unfair advantage or impose an unfair detriment on the opposing party if not estopped.
Id. at 29, 591 S.E.2d at 888-89 (internal quotation marks and citations omitted). Here, plaintiff takes the position that his marriage is voidable, a position clearly inconsistent with his sworn statements in the adoption proceedings. The court initially accepted plaintiff’s earlier assertion that he was married to defendant in permitting his adoption of defendant’s daughter. Although the second adoption order did not explicitly so find, it was based nonetheless on plaintiff’s sworn asser*198tion that he was married to defendant. Finally, plaintiff would impose an unfair detriment on defendant by undoing an eleven-year marriage were he allowed to proceed with his inconsistent position here. The trial court’s application of judicial estoppel was proper, and we affirm its denial of plaintiffs petition for annulment.
This opinion does not address and certainly does not validate any form of “common law marriage.” Neither party here claimed to have a common law marriage, and no such issue has been raised before this Court. Our decision is based only upon the application of judicial estoppel to the case before us.
Because we conclude that the trial judge properly denied annulment on grounds of judicial estoppel, we need not address plaintiffs other arguments or defendant’s cross-assignment of error.
Judge LEVINSON concurs.
Judge TYSON dissents in a separate opinion.