When the TMNT Adventures title from Archie was canceled in 1995, it was done abruptly and premature. A new story titled "The Forever War" had been already solicited for several months, but it didn't matter... the title went kaput. (For a little background on that story, check out these old posts from the 5th Turtle: Part 1, Part 2, Part 3, Part 4, Part 5.)
In recent years Mirage has teased us, saying that they would publish this "lost" story... but still, it never came. Until now!! Using the 25th anniversary as a pretty good excuse, wheels are really turning and "The Forever War" will finally see print! There's been a lack of details as to when and how we'd see it, but the answers seem to have finally arrived.
Cap e-mailed in with the above picture, which is a full-page advertisement for "The Forever War," stating it will (still) be in five parts and the first will be shipping in August (I think the previous best guess had been September). To make sure that your comic shop orders the book (and saves you a copy!) just print out the ad and bring it in to them - The information at the bottom will help ensure that they get it for you!
This scan is from the back of the Free Comic Book Day reprint of TMNT Vol. 1 #1 - Don't forget to visit your local comic shop on May 2nd to pick up your copy of that book!!