Charles Xavier’s heartbreaking last words in Logan hint at an unseen tragic event that happened in his past. James Mangold’s neo-Western actioner finally realized the grisly, blood-soaked potential of Wolverine’s on-screen adventures with a liberating R rating. All throughout the movie, Xavier is vaguely aware that he did something terrible, but his degenerative brain disease prevents him from remembering it, and Logan won’t tell him what happened. The audience is left to piece it together from hints that are dropped over the course of the movie, the effect that Xavier’s disease has on his mutant powers, and the harrowing confession in his death scene.

Logan primarily served as a bittersweet swansong for Hugh Jackman’s portrayal of Wolverine, but it also marked the end of the road for Patrick Stewart’s similarly beloved portrayal of Professor X. His Xavier is killed halfway through the movie by Logan’s sinister clone,...