Cube Shape seen during lightning flash

My wife and I were waiting out a strong storm with intense lightning this evening. While sitting in our living room with the lights off, she had fallen asleep and I was watching distant lightning from the window. During one of the lightning flashes, the sky was lit for a period of about 4-6 seconds, and I witnessed a cube like object above the tree tops between the lightning and myself. I can not say for certain whether it was directly across the road in the treetops or if it was farther away in the sky and appeared as if it was that close. But it was most definitely a cube shape soaring across the skyline. Black in color due to only seeing the shape, it had what appeared to be 4 sides, but appeared to tumble or rotate slightly. It appeared to be moving very quickly. I saw no lights or anything else during this time.