According to the August edition of Jump SQ this year, which will be released on July 4, 2016, Ao no Exorcist (Blue Exorcist) will be getting a sequel anime scheduled to air in 2017. It will adapt the Impure King arc from the manga.

The official website has recently displayed a countdown timer that is still running. The timer is scheduled to end on July 4.

The series previously received a first season anime adaptation in 2011 and a movie anime adaptation in 2012.

Official site: http://www.ao-ex.com/

Source: Otakomu

Update June 30
It was announced that the cast members from the first season will be reprised, while the staff members for director and series composition will be changed.

Director: Kouichi Hatsumi (Deadman Wonderland)
Series Composition: Toshiya Oono (Subete ga F ni Naru: The Perfect Insider)

Source: Nijipoi

Teaser


Ao no Exorcist: Kyoto Fujouou-hen on MAL