In a decision some gay-rights lawyers are calling a landmark, a state appeals court has recognized for the first time that New York state’s family law “presumption of legitimacy”—which says that a child born during a marriage is presumed to be both spouses’ child—applies to a child born to a same-sex married couple.

An Appellate Division, First Department, panel ruled that Han Ming T., the married partner of Marco D., a gay man now living in New York, should have been given notice of a petition to have their child adopted by Marco D.’s new gay partner.

The panel’s unanimous opinion affirmed the March 2016 decision from Manhattan Family Court Judge Stewart Weinstein. Weinstein had vacated the adoption of the “subject child,” in part because Ming T. was entitled to notice of the New York adoption proceeding and should have been heard before an adoption was granted.

“The child was born in 2014, as the result of jointly executed surrogacy agreements, at a time when the couple was considered legally married, thus giving rise to the presumption that the child is the legitimate child of both Marco and Ming,” the panel, consisting of Justices Peter Tom, Angela Mazzarelli, Richard Andrias, Jeffrey Oing and Anil Singh, wrote in their unsigned opinion.

“The child was born in wedlock, and Ming was entitled to notice of the adoption proceeding,” they added.

Lawyers for Ming T. said the panel’s ruling helps break legal ground in the First Department and, while not binding on the other three Appellate Division departments, may be followed by them as well. The attorneys also pointed out that there has been division, over the last decade or so, among the state’s lower courts about whether the “presumption of legitimacy” should apply to same-sex married partners.

Moreover, they said, the panel’s decision represents a logical following to the Court of Appeals’ landmark 2016 decision in Matter of Brooke S.B. v. Elizabeth A.C.C., in which the high court expanded the definition of “parenthood” in New York. In Brooke S.B., the high court ruled that the nonmarried, homosexual ex-partner of a biological parent could seek custody or visitation rights of children they once agreed to conceive and raise as co-partners with their exes.

In the case before the panel, Carlos A. v. Han Ming T., 4526A, the panel referenced Brooke S.B., and wrote, “Under the Court of Appeals’ most recent decision concerning parental standing (Matter of Brooke S.B. v Elizabeth A.C.C., 28 NY3d 1 [2016]), Ming’s claim to have standing as a parent is even stronger.”

Linda Genero Sklaren, a partner at Warsaw Burstein in Manhattan who helped brief the Ming T. appeal, said on Thursday that the panel’s decision is “another step toward true marriage equality.”

“Most importantly, it’s a victory for children of same-sex marriages,” she said, “because it protects their rights to continue their relationships with both of their same-sex parents.”

Sklaren also pointed out that a state appeals court recognizing the “presumption of legitimacy” for same-sex married couples was particularly important because “with technology as it is today [for surrogate births] for same-sex couples, both spouses in same-sex marriage are not going to be biologically related to a child.”

“The nonbiological spouse now has rights, and that child is presumed to be the legitimate child of both parents,” Sklaren, who also helped brief the appeal in Brooke S.B., said.

Frederick Magovern, of Magovern & Sclafani in Mineola, New York, represented Marco D. and his new partner, Carlos A. He could not be reached for comment Thursday.

Sklaren said that counsel for Marco D. and Carlos A. has said that they intend to seek leave to appeal the First Department’s ruling.

The dispute between Ming T. and Carlos A. has been a winding one, and it was laid out by the panel in the first half of its Sept. 28 opinion.

Marco D. and Ming T., both British citizens, entered a civil union in the United Kingdom in 2008. They converted that into a legal marriage in 2015, effective as of the date of their civil union

In 2013, the panel wrote, the couple, both wanting to become parents, signed an egg donor and surrogacy agreement and both contributed sperm.

An embryo fertilized by only Marco D.’s sperm was transferred to the surrogate.

The resulting child, born in September 2014, was named after both Marco D.’s and Ming T.’s mothers.

The couple initiated a proceeding in Missouri to terminate the egg donor and surrogate’s parental rights to the child, and, in October 2014, a Missouri court awarded the genetic father, Marco D., “sole and exclusive custody” of the child.

Marco D., Ming T. and the child then lived in Florida as a family until October 2015, when Ming T. moved to the U.K. to seek employment.

Marco D. began a relationship with Carlos A. at some point after 2013, and the new couple moved to New York with the child after Ming T. went to the U.K.

In January 2016, Carlos A. petitioned in New York to adopt the child, but in papers was untruthful and said that Marco D. and Ming T. had not lived together continuously since 2012 and that Carlos A. and Marco D. had been caring for the child since her birth.

Ming T.’s role in the surrogacy process was not disclosed to the family court, nor was a Florida divorce action commenced by Ming T. in March 2016 in which he sought joint custody of the child.

The family court granted the adoption petition in May 2016 but it was later vacated.

The panel also ruled, in addition to the notice-of-proceeding rights due to Ming T., that the “petitioner’s [Carlos A.'s] failure to disclose the Florida divorce action, in which the child was named as a child of the marriage and Ming T. sought joint custody, provided another ground to vacate the adoption (see Domestic Relations Law § 114[3]).”

Ming T.’s adoption counsel and appellate counsel was Nina Rumbold, of Rumbold & Seidelman in Bronxville, New York. Sklaren and Charlotte Licker, an attorney with Gottesman, Wolgel, Flynn, Weinberg & Lee in Manhattan, were of counsel to Rumbold in the appeal, Sklaren said.