For a while now, we've known the Arrowverse -- which consists of CW's "Supergirl," "The Flash," "Arrow," and "DC's Legends of Tomorrow" -- is set to crossover next month to fight the menacing Dominators in a four-night event titled “Invasion!" Well, as revealed in a social media post today, one major hero featured in the crossover is doing their homework, researching the source material from which the TV event is based.RELATED: New CW Crossover Promo Promises Best Team-Up Ever!Actor David Harewood, who plays Hank Henshaw/Martian Manhunter in "Supergirl," shared an image on his Twitter account of himself reading the "Invasion!: Secret No More" trade paperback with the quote, "Invasion!!!! #HeroesVAliens #SupergirlCW #Crossover."

"Invasion!: Secret No More" collects "Invasion!" #1-3 and is written by Keith Giffen and Bill Mantlo, with art by Todd McFarlane and Bart Sears. It tells the story of Earth's greatest superheroes repelling an attack from a group of alien races. The CW event will follow the same principles, with an alien race called the Dominators looking to conquer our Earth.

The crossover begins Monday, Nov. 28, on the midseason finale of “Supergirl,” and continues Tuesday, Nov. 29, on “The Flash” and Wednesday, Nov. 30, on “Arrow” before concluding Thursday, Dec. 1, on “DC’s Legends of Tomorrow.”