Dylan O'Brien plays identical twin brothers in Twinless.
O'Brien knew he had to be a part of Twinless because he felt like "this could be something so special" where he could really "go on the journey with these characters that I felt such a connectivity to in hands that I trusted so much," referring to Sweeney.
Sweeney himself is not a twin, though he says, "I am still waiting to be running into a forest one day and bump into it."