It's Always Sunny in Philadelphia returned with a crossover with Abbott Elementary, and its most shocking moment is explained by one star.

The long-running TV comedy series, “It’s Always Sunny in Philadelphia,” returns Wednesday, July 9 at 9 p.m. ET on FXX.

When the narcissistic gang from "It’s Always Sunny in Philadelphia" visited the "Abbott Elementary" school in a crossover episode earlier this year, audiences got to see the two Philly TV universes collide in hilarious ways — all while keeping the episode PG for "Abbott’s" more family-oriented viewers.