NASA Boeing X-48C Makes Maiden Flight

While the articles at the links below doesn't provide many details regarding the test objectives, flights at a similar point in the X-48B test program focused on controllability in the heart of the flight envelope.  The two planes look a lot alike, but the C goes with only two engines and a more conventional "Bonanza-style" V-tail.  For you historically-minded readers, can anyone tell me when the last (unclassified) manned X-Plane flew and what its designation was?  Most recent "X's" have been UAVs.

http://news.cnet.com/8301-11386_3-57488507-76/nasas-futuristic-x-48c-hybrid-wing-body-plane-takes-flight/

http://www.redorbit.com/news/space/1112671679/nasa-x-48c-flight-080812/