The news was revealed at Comic-Con on Sunday by executive producer Bob Singer.
Details are currently sketchy, but according to TVLine , a new character will be introduced in or around episode 20 of Supernatural season nine and that episode will serve as a “planted” pilot for the new show (it’s the same model used by The Vampire Diaries to launch The Originals this year). The new character will be the star of the spin-off.
The new show will also apparently be city-based. We’ll probably get to see it in the UK sometime around 2018…
More news as we get it.