Talk About Seeing Double: High School Graduating Class Has 'Unprecedented' 9 Sets of Twins

These teens will make you do a double take — or nine of them.

Read: Rare, Identical Quadruplets Snooze Their Way Through Precious Photo Shoot

That's the number of twins who walked across the stage at a Long Island high school graduation Sunday.

"I didn't know there were that many twins graduating until graduation day," Melissa LoCascio, joined by sister Amanda LoCascio, told InsideEdition.com.

When East Meadow High School principal Rich Howard asked the 18 twins to stand, Melissa and Amanda rose with Francisca and Vilma Fuentes, George and Mathew Kalambukad, Benjamin and Danielle Levy, Emily and Nathaniel Mendelson, Danielle and Frank Michelini, Molli and Mackenzie Salomon, Jacquelyn and Jonathan Tams, and Jake and Jesse Weiner.

According to Howard, the school has never seen so many twins in a graduating class, although he is unsure of the official record.

He first realized that there were 18 twins in the graduating class of 421 seniors when Mackenzie Salomon, who worked on the yearbook, wanted to do a spread of all the twins in the class.

But Amanda LoCascio told InsideEdition.com that she started asking questions much earlier when she noticed several people in their town who were born in their year were twins.

"Mom, 1998, what was going on?" Amanda joked.

In fact, most of the twins had even gone to elementary school together, except the Fuentes sisters, who transferred to the high school in 2014.

Read: A Set of Twins Married Another Set of Twins... and the Priests and Flower Girls Were Twins, Too

The community of twins is so tight knit that Mackenzie Salomon even went to prom with Jesse Weiner, even though her sister Molli told InsideEdition.com that she opted out of going with Jake Weiner, and went with her significant other instead.

Watch: Mother and Son Graduate High School Together: 'Being On Stage With My Mom Was Surreal'