A Morris County school district is apologizing for a substitute teacher who told first-grade students that Santa Claus isn't real.

Cedar Hill School Principal Michael Raj sent a letter to parents following the incident Thursday at the school in Montville. Raj noted that as a parent himself, he understands the "sensitive nature" of the topic.

At least one parent told News 12 New Jersey that her 6-year-old daughter Addriana was extremely upset by the ordeal.

“I was heartbroken. You know, my daughter is the hugest believer in the whole Christmas spirit - Santa, giving,” says Myra Sansone-Aboyoun.

Sansone-Aboyoun says that she assured her daughter that, yes, there is a Santa Claus.

Montville Schools Superintendent Rene Rovtar said in a statement that she was "troubled and disheartened by this incident." Rovtar explained that "childhood wonder associated with all holidays and traditions" is special to her.

News 12 New Jersey went in search of proof that Santa does exist – and found it in nearby Morristown. Proof of Santa's history is on the walls of a museum in MacCollugh Hall. Legendary 19th century cartoonist Thomas Nast made Santa world famous when he lived up the street. The cartoons Nast drew are part of a monthlong exhibit.

The Cedar Hill School principal says he has spoken with the teacher about her "poor judgment." Administrators haven't released the teacher's name or said if she would be allowed to work again in the district.