Saints Row IV has been confirmed via the series' Facebook page with a picture of the game's logo and a simple message: "We're BACK!"
Seeing as the game was being discussed openly by former publishers THQ around the same time as Saints Row the Third was released in 2011, this news shouldn't come as a surprise, but it's probably still a relief to anyone worried about whether the series would survive THQ's bankruptcy and the IP's subsequent purchase by Koch/Deep Silver.
No word yet on additional details, but Tweets from those in the know suggest that all will be revealed next week (September 22nd or 23rd) at PAX East, with the game reaching stores sometime in August.
UPDATE: We have a release date (coming to PS3, Xbox 360 and PC August 20, 2013 in North America, and August 23, 2013 for those same platforms the rest of the world) and a suitably awesome teaser trailer now as well!
UPDATE #2: According to a Deep Silver press release, the new game will feature superpowered Saints fighting off an alien invasion.