Officially announced on their website, Frozenbyte released an announcement trailer (seen above) and stated that it will launch on PC first, followed by other platforms.
Frozenbyte also wants you to know that if you missed the first two games, they are current on sale for 85% off on Steam until March 14th!
I have never REALLY played the Trine series. My only foray into that magical universe is the first 20 minutes of Trine 2 on PlayStation 4, which I immediately stopped because I was sidetracked. After seeing the screenshots and announcement trailer for Trine 3 though, I am seriously considering actually taking the time to play Trine 2 now. It looks awesome!