Frozenbyte have now officially announced Trine 4: The Nightmare Prince, although some fans were already aware of the new title thanks to a leak earlier in October 2018. The developers stated it should arrive at some point in 2019.
Frozenbyte's hand may have been somewhat forced in this announcement, as Trine 4 was inadvertently leaked or announced, depending how you look at it, by none other than European Union. The leaky document was quickly removed, but the development of Trine 4 was already made public, so some promotional material was sure to follow.
This resulted in Frozenbyte posting a teaser for the game, announcing it will come next year for PC, PlayStation 4, Xbox One and Nintendo Switch. The last one should be a good call in particular, as the nature of Trine is a perfect fit for portable gaming since it never required a monster rig to run and it's a fun platformer with puzzles set on a beautiful background.
Not all Trines were well received though - Trine 3 sent brought a heap of trouble for the developers since the game appeared to be unfinished and the ending was not satisfying. Frozenbyte's woes continued with Has-Been Heroes and Shadwen also failing to find an audience, but now it seems like Modus Game breathed some life into the studio as they partnered up for Trine 4.
That's a nice way of saying the publisher most likely injected a hefty amount of money into the development of Trine 4, just like European Union did, as you can see on the article linked above. It seems like Frozenbyte consider this to be just a minor teaser for an official announcement that should happen soon.
Let's keep fingers crossed for gameplay footage, and most importantly - hope for a return to the roots of Trine, in a 2D setting with beatiful, vibrant backgrounds. This is entirely possible as the developers have even apologised to fans via a video for Trine 3, and hopefully learned from their mistakes.