A state Supreme Court justice in Central Islip granted three adults “tri-custody” of their 10-year-old son, a ruling the plaintiff’s lawyer says is likely the first of its kind in New York.

The case involved a child who has two mothers and a father.

A Long Island couple married since 1994, identified in court papers as Dawn M. and Michael M., had tried unsuccessfully to have a child before they met Audria G., a downstairs neighbor who lived there with her boyfriend.

The two women forged a close friendship in 2001 and when Audria G.’s boyfriend moved out, the woman moved in upstairs, court documents state. The three began an “intimate” relationship sometime in 2004, soon considered themselves “a family,” and planned on having a child together. Audria gave birth to the boy, known as J.M. in court papers, in 2007, according to the March 8 ruling.

The judge’s ruling came after the married couple’s relationship dissolved and the two women moved out of the home with the child. The nonbiological mother of the child sought shared custody.

Justice Patrick Leis III said his decision “is the logical evolution” of 2011’s federal Marriage Equality Act and of a state Court of Appeals case from last year that permitted adoptive or nonbiological parents to establish standing and petition for custody and visitation with a child. That case determined it is up to a trial court to determine whether or not granting such rights is in the best interest of the child.

While Dawn M., Audria G. and the child continue to live together, Dawn M. sought a custody agreement that included her “because she fears that without court-ordered visitation and shared custody, her ability to remain in J.M.’s life would be solely dependent upon obtaining the consent of either Audria” or Michael, the decision states.

“This court finds credible the testimony of Audria and plaintiff that J.M. was raised with two mothers and that he continues to the present day to call both ‘mommy,’” the decision reads. “J.M. is a well adjusted ten-year-old boy who loves his father and his two mothers.”

The case was heard during a three-day-long trial in October. The judge granted Dawn M. time alone with J.M. every Wednesday for dinner, as well as a weeklong school recess and two weeks out of the summer.

“She is very thankful and relieved,” attorney Karen G. Silverman of Commack said of Dawn M. in a phone interview Wednesday. “She was very concerned about her continuing rights with regard to her son who she has been a mother of since birth.”

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Michael M. will continue to get shared custody and has time with his son three weekends a month. Defense attorney Kenneth J. Molloy of Central Islip said both he and his client are “quite disappointed with the results” and said will appeal.

“The judge has diminished the meaning of ‘parents,’” Molloy said. “Our argument is that you can only have two parents. He’s created three parents and there’s no legal basis for it.”

In Leis’ ruling, he took into consideration that Dawn M.’s medical insurance that was used to cover Audria’s care during pregnancy and delivery, and that the two “shared duties as J.M.’s mother,” including the women both taking J.M. to doctor’s appointments and taking turns waking up in the night to feed him.