The actors reprised their roles as Tris, Uriah, Christina and Johanna on set in Atlanta on June 8, 2015.
Elgort is back as Tris' brother, Cale, who is put on trial for assisting former Erudite leader Jeanine Matthews (Kate Winslet).
Veronica Roth's novel, Allegiant, was divided into two parts. The films are scheduled for release on March 18, 2016 and March 24, 2017.
Without revealing any spoilers, Woodley tells E! News that the ending of Allegiant is "awesome."
Jeff Daniels (not pictured) was cast in the final two films in the series.
Production on the third film began May 18, and four days later, Elgort Instagrammed a picture from "stunt rehearsal."
Theo James, Miles Teller, Maggie Q and Naomi Watts (not pictured) are also reprising their roles in the film.
Once he was on set, the actor tweeted a picture of the "dystopian future" ahead.
Robert Schwentke (not pictured) is directing the final two films in the Divergent series.