New Line Cinema was developing the film waaay back in the early 2000s before it was absorbed by WB so they still have their hands on the project. It's been in development hell with writers and directors coming and going for years. It was later added to the DCEU slate, and yes it is part of the DCEU.
Asher Angel will play Billy Barton in the movie
Stick "we work together and we get out of here alive"
Matt "peace out suckas"