It was found by amateur astronomers Marcel Drechsler and Xavier Strottner.
According to the above articles, it's pretty big:
With an extension of 44 x 36 arc minutes, StDr56 is not only the largest probable PN in the region, but in the night sky it covers more than half of the area of the famous Triangulum Galaxy M33, which is located only a few degrees from Strottner-Drechsler 56.
It’s about the same size as the full Moon on the sky.
So, if it's so big, why was it only discovered now? Wouldn't it make sense if all large objects were already discovered a long time ago?