This week's "Abbott Elementary" episode is just half of the story. "Volunteers" featured the long-awaited crossover with FX's long-running "It's Always Sunny in Philadelphia," as told from the vantage point of the hit ABC sitcom.

After much anticipation, the unlikely meeting of the two worlds unfolded on Wednesday's installment of "Abbott Elementary."

The two sitcoms could hardly be more tonally different, but this week’s crossover episode of “Abbott” was relatively seamless.

The highly anticipated crossover episode of “Abbott Elementary” and “It’s Always Sunny in Philadelphia” blends the raunchy, NSFW style of the FX show with the witty, family-friendly romp.

Fan reactions to the 'Abbott Elementary' and 'It's Always Sunny in Philadelphia' crossover show that it was the strange combo they needed.

The cast of "It's Always Sunny in Philadelphia" will appear on "Abbott Elementary" tonight. Here's how to watch, when it airs and what to know about the crossover.