'Arrow' season 5 spoilers: EP teases episode 100; photos reveal Oliver's wedding, dead characters

"Arrow" season 5 will mark a major milestone this month with its 100th episode airing as part of The CW's four-way crossover.

100th episodes have always been a big deal, as have the 100th issues of comic books, which means that the "Arrow" team must have something special and game-changing planned.

"Arrow" executive producer Marc Guggenheim recently spoke to Entertainment Weekly about the show's upcoming 100th episode, saying, "It feels like the 100th issue of a comic book, perhaps even more so than the 100th episode of a television show."

EW notes that this comment is a bit worrying, as important characters tend to be killed off during milestone episodes or comics issues. As "The Walking Dead" fans know, the fan-favorite character Glenn met a tragic end in the 100th issue of Robert Kirkman's "Walking Dead" comics.

Guggenheim further hinted that something potentially upsetting may be in store in episode 100, telling the outlet, "You know me, I always want everyone worried."

The 100th episode of "Arrow" drops midway in The CW's four-night crossover, in which Arrow/Oliver Queen (Stephen Amell) appears alongside Supergirl (Melissa Benoist), The Flash (Grant Gustin), and the Legends of Tomorrow.

This week, The CW released the synopsis and the first photos from "Invasion!," the "Arrow" episode, and it surprisingly reveals Oliver's wedding, as well as the return of characters who have long ago died.

According to the "Invasion!" synopsis, Oliver will wake up in an alternate timeline in which Moira Queen (Susanna Thompson) and Robert Queen (Jamey Sheridan) are alive and he is engaged to Laurel (Katie Cassidy). While everything seems perfectly fine, he begins to notice tiny imperfections that lead him to question his reality. As Oliver grapples with his new situation, Felicity (Emily Bett Rickards) and the rest of Team Arrow get help from The Flash and Supergirl as they face a new villain.

"Arrow" season 5 airs Wednesdays at 8 p.m. EST on The CW.