The family of a beloved New Jersey principal who died while donating bone marrow to save a boy’s life has filed suit against the hospital where he underwent the failed procedure.

Westfield High School principal Derrick Nelson, 44, had visited Hackensack University Medical Center in February to help the French 14-year-old in his fight against cancer, according to a lawsuit filed Monday in Union County Superior Court.

While undergoing the procedure, Nelson was given anesthesia despite having an insufficient amount of oxygen in his body, which was a “breach of the standard to care,” according to the suit.

The suit — which accuses the hospital of negligence — says physicians ignored signs that he was suffering from hypoxemia, which involves low levels of oxygen in the blood.

When physicians did act, they allegedly gave Nelson a mask but didn’t provide him enough oxygen, which led him to suffer “severe brain damage,” the suit said.

He fell into a coma and died weeks later from the brain injury.

“As a direct and proximate result of defendants’ malpractice, Derrick Nelson experienced great pain, suffering and permanent injury, ultimately resulting in his untimely death,” the suit said.

His fiancée, Sheronda Braker, who shares a daughter with Nelson, is suing for unspecified damages from Hackensack University Medical Center and others.

The suit also names Dr. Jerry Baratta, Hackensack Anesthesiology Associates of New Jersey Healthcare Specialists and unnamed doctors and nurses involved in Nelson’s care.

When asked to comment on the suit, Dr. Andrew Goy, chair of the hospital’s John Theurer Cancer Center, said: “We are unable to say more at this time due to the litigation process; however, we have been in communication with the family through their legal representation. It is important to note that the safety of our patients is and will remain our primary focus and we have one of the largest and most experienced bone marrow transplantation programs in the country.”

Requests for comment from Baratta and Anesthesiology Associates weren’t immediately returned.