But, for Shyamalan obsessives, the twist is a revelation, a neat bit of fan service, and an answer to years of speculation. Not long after Unbreakable's release, the secretive filmmaker began to discuss the possibility of one day making a sequel. It turns out, according to an interview with The Hollywood Reporter, the Kevin character in Split was originally a part of the Unbreakable script. "I pulled him out, because it just wasn't balancing right," he explains. "But a bunch of the scenes that are in this movie, I wrote 15 years ago."
As shocking as the ending is, it also makes a twisted sort of sense. More than his mega-hits like The Sixth Sense and Signs, Unbreakable is the Shyamalan film with the most devoted cult following. A large part of its appeal is in the way the movie toys with genre conventions by telling a superhero origin story in a restrained, subdued style. Similarly, Split is a Silence of the Lambs-style thriller that, in its final moment, reveals itself to be a portrait of a comic book villain. It redefines what comes before it by playing with a formal feature of modern superhero films: the post-credits "tag" scene you often see in Marvel films.